Estoppel is a judicial device in common law legal systems whereby a court may prevent or "estop" a person from making assertions or from going back on his or her word; the person being sanctioned is "estopped". Estoppel may prevent someone from bringing a particular claim. Legal doctrines of estoppel are based in both common law and equity. It is also a concept in international law.

Types of estoppel.

There are many different types of estoppel which can arise, but the common thread between them is that a person is restrained from asserting a particular position in law where it would be inequitable to do so. By way of illustration:

If a landlord promises the tenant that he will not exercise his right to terminate a lease, and relying upon that promise the tenant spends money improving the premises, the doctrine of promissory estoppel may prevent the landlord from exercising a right to terminate, even though his promise might not otherwise have been legally binding as a contract. The landlord is precluded from asserting a specific right.

If a person brings legal proceedings in one country claiming that a second person negligently injured them and the courts of that country determine that there was no negligence, then under the doctrine of issue estoppel the first person will not normally be able to argue before the courts of another country that the second person was negligent (whether in respect of the same claim or a related claim). The first person is precluded from asserting a specific claim.

Estoppel is an equitable doctrine. Accordingly, any person wishing to assert an estoppel must normally come to the court with "clean hands".

The doctrine of estoppel (which may prevent a party from asserting a right) is often confused with the doctrine of waiver (which relates to relinquishing a right once it has arisen). It also substantially overlaps with, but is distinct from, the equitable doctrine of laches.

A lien is a form of security interest granted over an item of property to secure the payment of a debt or performance of some other obligation. The owner of the property, who grants the lien, is referred to as the lienee and the person who has the benefit of the lien is referred to as the lienor or lien holder.

The etymological root is Anglo-French lien, loyen "bond", "restraint", from Latin ligamen, from ligare "to bind".

In the United States, the term lien generally refers to a wide range of encumbrances and would include other forms of mortgage or charge. In the US, a lien characteristically refers to nonpossessory security interests (see generally: Security interest—categories).

In other common-law countries, the term lien refers to a very specific type of security interest, being a passive right to retain (but not sell) property until the debt or other obligation is discharged. In contrast to the usage of the term in the US, in other countries it refers to a purely possessory form of security interest; indeed, when possession of the property is lost, the lien is released. However, common-law countries also recognize a slightly anomalous form of security interest called an "equitable lien" which arises in certain rare instances.

Despite their differences in terminology and application, there are a number of similarities between liens in the US and elsewhere in the common-law world.

Salary.

As of 2018, associate justices receive a yearly salary of $255,300 and the chief justice is paid $267,000 per year. Article III, Section 1 of the U.S. Constitution prohibits Congress from reducing the pay for incumbent justices. Once a justice meets age and service requirements, the justice may retire. Judicial pensions are based on the same formula used for federal employees, but a justice's pension, as with other federal courts judges, can never be less than their salary at the time of retirement.

Judicial leanings.

Although justices are nominated by the president in power, and receive confirmation by the Senate, justices do not represent or receive official endorsements from political parties, as is accepted practice in the legislative and executive branches. Jurists are, however, informally categorized in legal and political circles as being judicial conservatives, moderates, or liberals. Such leanings, however, generally refer to legal outlook rather than a political or legislative one. The nominations of justices are endorsed by individual politicians in the legislative branch who vote their approval or disapproval of the nominated justice. The ideologies of jurists can be measured and compared with several metrics, including the Segal–Cover score, Martin-Quinn score, and Judicial Common Space score.

Following the confirmation of Amy Coney Barrett in 2020, the Court currently consists of six justices appointed by Republican presidents and three appointed by Democratic presidents. It is popularly accepted that Chief Justice Roberts and associate justices Thomas, Alito, Gorsuch, Kavanaugh, and Barrett appointed by Republican presidents, compose the Court's conservative wing. Justices Breyer, Sotomayor and Kagan, appointed by Democratic presidents, compose the Court's liberal wing. Gorsuch had a track record as a reliably conservative judge in the 10th circuit. Kavanaugh was considered one of the more conservative judges in the DC Circuit prior to his appointment to the Supreme Court. Likewise, Barrett's brief track record on the Seventh Circuit is conservative. Prior to Justice Ginsburg's death, Chief Justice Roberts was considered the Court's median justice (in the middle of the ideological spectrum, with four justices more liberal and four more conservative than him), making him the ideological center of the Court.

In eyewitness identification, in criminal law, evidence is received from a witness "who has actually seen an event and can so testify in court".

The Innocence Project states that "Eyewitness misidentification is the single greatest cause of wrongful convictions nationwide, playing a role in more than 75% of convictions overturned through DNA testing." This non-profit organization uses DNA evidence to reopen criminal convictions that were made before DNA testing was available as a tool in criminal investigations.

Even before DNA testing revealed wrongful convictions based on eyewitness identifications, courts recognized and discussed the limits of eyewitness testimony. The late U.S. Supreme Court Justice William J. Brennan, Jr. observed in 1980 that "At least since United States v Wade, 388 U.S. 218 (1967), the Court has recognized the inherently suspect qualities of eyewitness identification evidence, and described the evidence as "notoriously unreliable", while noting that juries were highly receptive to it. Similarly, in the United Kingdom, the Criminal Law Review Committee, writing in 1971, stated that cases of mistaken identification "constitute by far the greatest cause of actual or possible wrong convictions".

Historically, Brennan said that "All the evidence points rather strikingly to the conclusion that there is almost nothing more convincing  than a live human being who takes the stand, points a finger at the defendant, and says 'That's the one!'" Another commentator observed that the eyewitness identification of a person as a perpetrator was persuasive to jurors even when "far outweighed by evidence of innocence."

Gambling (also known as betting) is the wagering of money or something of value (referred to as "the stakes") on an event with an uncertain outcome, with the primary intent of winning money or material goods. Gambling thus requires three elements to be present: consideration (an amount wagered), risk (chance), and a prize. The outcome of the wager is often immediate, such as a single roll of dice, a spin of a roulette wheel, or a horse crossing the finish line, but longer time frames are also common, allowing wagers on the outcome of a future sports contest or even an entire sports season.

The term "gaming" in this context typically refers to instances in which the activity has been specifically permitted by law. The two words are not mutually exclusive; for example, a "gaming" company offers (legal) "gambling" activities to the public and may be regulated by one of many gaming control boards, for example, the Nevada Gaming Control Board. However, this distinction is not universally observed in the English-speaking world. For instance, in the United Kingdom, the regulator of gambling activities is called the Gambling Commission (not the Gaming Commission). The word gaming is used more frequently since the rise of computer and video games to describe activities that do not necessarily involve wagering, especially online gaming, with the new usage still not having displaced the old usage as the primary definition in common dictionaries. "Gaming" has also been used to circumvent laws against "gambling". The media and others have used one term or the other to frame conversations around the subjects, resulting in a shift of perceptions among their audiences.

Gambling is also a major international commercial activity, with the legal gambling market totaling an estimated $335 billion in 2009. In other forms, gambling can be conducted with materials which have a value but are not real money. For example, players of marbles games might wager marbles, and likewise games of Pogs or Magic: The Gathering can be played with the collectible game pieces (respectively, small discs and trading cards) as stakes, resulting in a meta-game regarding the value of a player's collection of pieces.

Penal damages are liquidated damages which exceed reasonable compensatory damages, making them invalid under common law. While liquidated damage clauses set a pre-agreed value on the expected loss to one party if the other party were to breach the contract, penal damages go further and seek to penalise the breaching party beyond the reasonable losses from the breach. Many clauses which are found to be penal are expressed as liquidated damages clauses but have been seen by courts as excessive and thus invalid.

The judicial approach to penal damages is conceptually important as it is one of the few examples of judicial paternalism in contract law. Even if two parties genuinely and without coercion wish to consent to a contract which includes a penal clause, they are unable to. So, for example, a person wishing to give up smoking cannot contract with a third party to be fined $100 each time they smoke as this figure does not represent the expectation loss of the contract.

A wholesale review of the English law rule against penalty clauses (as opposed to penal damages) was conducted by the UK Supreme Court in the 2015 judgment in Cavendish Square Holding BV v Talal El Makdessi. 

In contract law, rescission is an equitable remedy which allows a contractual party to cancel the contract. Parties may rescind if they are the victims of a vitiating factor, such as misrepresentation, mistake, duress, or undue influence. Rescission is the unwinding of a transaction. This is done to bring the parties, as far as possible, back to the position in which they were before they entered into a contract (the status quo ante).

A quasi-contract (or implied-in-law contract or constructive contract) is a fictional contract recognized by a court. The notion of a quasi-contract can be traced to Roman law and is still a concept used in some modern legal systems.

The rule against perpetuities is a legal rule in the Anglo-American common law that prevents people from using legal instruments (usually a deed or a will) to exert control over the ownership of private property for a time long beyond the lives of people living at the time the instrument was written. Specifically, the rule forbids a person from creating future interests (traditionally contingent remainders and executory interests) in property that would vest beyond 21 years after the lifetimes of those living at the time of creation of the interest, often expressed as a “life in being plus twenty-one years”. In essence, the rule prevents a person from putting qualifications and criteria in a deed or a will that would continue to affect the ownership of property long after he or she has died, a concept often referred to as control by the "dead hand" or "mortmain".

The basic elements of the rule against perpetuities originated in England in the 17th century and were "crystallized" into a single rule in the 19th century. The rule's classic formulation was given in 1886 by the American legal scholar John Chipman Gray:

No interest is good unless it must vest, if at all, not later than twenty-one years after some life in being at the creation of the interest.

— John Chipman Gray, Rule Against Perpetuities § 201.

In the common law of England, the doctrine of worthier title was a legal doctrine that preferred taking title to real estate by descent over taking title by devise or by purchase. It essentially provides that a remainder cannot be created in the grantor's heirs, at least not by those words.

The rule provided that where a testator undertook to convey an heir the same estate in land that the heir would take under the laws of inheritance, the heir would be adjudged to have taken title to the land by inheritance rather than by the conveyance, because descent through the bloodline was held to be "worthier" than a conveyance through a legal instrument.

A restraint on alienation, in the law of real property, is a clause used in the conveyance of real property that seeks to prohibit the recipient from selling or otherwise transferring his interest in the property. Under the common law such restraints are void as against the public policy of allowing landowners to freely dispose of their property. Perhaps the ultimate restraint on alienation was the fee tail, a form of ownership which required that property be passed down in the same family from generation to generation, which has also been widely abolished.

The Rule in Shelley's Case is a rule of law that may apply to certain future interests in real property and trusts created in common law jurisdictions. It was applied as early as 1366 in The Provost of Beverly's Case but in its present form is derived from Shelley's Case (1581), in which counsel stated the rule as follows:

…when the ancestor by any gift or conveyance takes an estate of freehold, and in the same gift or conveyance an estate is limited either mediately or immediately to his heirs in fee simple or in fee tail; that always in such cases, 'the heirs' are words of limitation of the estate, not words of purchase.

The Supreme Court of the United States (SCOTUS) is the highest court in the federal judiciary of the United States of America. It has ultimate (and largely discretionary) appellate jurisdiction over all federal and state court cases that involve a point of federal law, and original jurisdiction over a narrow range of cases, specifically "all Cases affecting Ambassadors, other public Ministers and Consuls, and those in which a State shall be Party". The Court holds the power of judicial review, the ability to invalidate a statute for violating a provision of the Constitution. It is also able to strike down presidential directives for violating either the Constitution or statutory law. However, it may act only within the context of a case in an area of law over which it has jurisdiction. The Court may decide cases having political overtones, but it has ruled that it does not have power to decide non-justiciable political questions.

Established by Article Three of the United States Constitution, the composition and procedures of the Supreme Court were initially established by the 1st Congress through the Judiciary Act of 1789. As later set by the Judiciary Act of 1869, the Court consists of the chief justice of the United States and eight associate justices. Each justice has lifetime tenure, meaning they remain on the Court until they resign, retire, die, or are removed from office. When a vacancy occurs, the president, with the advice and consent of the Senate, appoints a new justice. Each justice has a single vote in deciding the cases argued before it. When in majority, the chief justice decides who writes the opinion of the court; otherwise, the most senior justice in the majority assigns the task of writing the opinion.

The Court meets in the Supreme Court Building in Washington, D.C. Its law enforcement arm is the Supreme Court Police.

Exculpatory evidence is evidence favorable to the defendant in a criminal trial that exonerates or tends to exonerate the defendant of guilt. It is the opposite of inculpatory evidence, which tends to present guilt.

In many countries, including the United States, police and prosecutors are required to disclose to the defendant exculpatory evidence they possess before the defendant enters a plea (guilty or not guilty).

Per the Brady v Maryland decision, prosecutors have a duty to disclose exculpatory evidence even if not requested to do so. While the prosecution is not required to search for exculpatory evidence and must disclose only the evidence in its possession, custody, or control, the prosecution's duty is to disclose all information known to any member of its team, for example, police, investigators, crime labs, et cetera. In Brady v Maryland, the U.S. Supreme Court held that such a requirement follows from constitutional due process and is consistent with the prosecutor's duty to seek justice.

Inculpatory evidence is evidence that shows, or tends to show, a person's involvement in an act, or evidence that can establish guilt. In criminal law, the prosecution has a duty to provide all evidence to the defense, whether it favors the prosecution's case or the defendant's case. Evidence that tends to show a person's innocence is considered exculpatory evidence.

For example, if a man is poisoned to death by an overdose of arsenic, and a bottle of arsenic is found in the purse of his wife, that bottle could be considered inculpatory evidence against his wife. The bottle of arsenic in his wife's purse could also be considered exculpatory evidence, tending to show the man's innocence as far as suicide is concerned.

Demonstrative evidence is evidence in the form of a representation of an object. This is, as opposed to, real evidence, testimony, or other forms of evidence used at trial.

A lie is a statement used intentionally for the purpose of deception. The practice of communicating a lie is called lying; a person who communicates a lie may be termed a liar. Lies may be employed to serve a variety of instrumental, interpersonal, or psychological functions for the individuals who use them. Generally, the term "lie" carries a negative connotation and, depending on the context, a person who communicates a lie may be subject to social, legal, religious, or criminal sanctions.

Payola, in the music industry, is the illegal practice of payment to commercial radio in which the song is presented as being part of the normal day's broadcast, without announcing that there has been consideration paid in cash or in kind for its airplay adjacent to the recording's broadcast. Under US law, a radio station can play a specific song in exchange for money, but this must be disclosed on the air as being sponsored airtime.

The term has come to refer to any undisclosed payment made to cast a product in a favorable light (such as obtaining positive reviews). Some radio stations report spins of the newest and most popular songs to industry publications. The number of times the songs are played can influence the perceived popularity of a song.

The term payola is a combination of "pay" and "ola", a common suffix of product names in the early 20th century, such as Pianola, Victrola, Amberola, Crayola, Rock-Ola, Shinola, or brands such as the radio equipment manufacturer Motorola. Payola has come to mean the payment of a bribe in commerce and in law to say or do a certain thing against the rules of law, but more specifically a commercial bribe. The FCC defines "payola" as a violation of the sponsorship identification rule.

Pickpocketing is a form of larceny that involves the stealing of money or other valuables from the person or a victim's pocket without them noticing the theft at the time. It may involve considerable dexterity and a knack for misdirection. A thief who works in this manner is known as a pickpocket.

As an occupation.

Pickpockets and other thieves, especially those working in teams, sometimes apply distraction, such as asking a question or bumping into the victim. These distractions sometimes require sleight of hand, speed, misdirection and other types of skills.

Pickpockets may be found in any crowded place around the world. However, Barcelona and Rome were recently singled out as being particularly dangerous pickpocket havens. Thieves have been known to operate in high traffic areas such as mass transit stations, even boarding subway trains so they can use the distractions of crowds and sudden stop-and-go movements from the train to steal from others. As soon as the thieves have what they want, they simply get off at the next stop leaving the victim unable to figure out who robbed them and when.