An interest in possession trust is a trust in which at least one beneficiary has the right to receive the income generated by the trust (if trust funds are invested) or the right to enjoy the trust assets for the present time in another way. The beneficiary with the right to enjoy the trust property for the time being is said to have an interest in possession and is colloquially described as an income beneficiary, or the life tenant.

Beneficiaries of a trust have an interest in possession if they have the immediate and automatic right to receive the income arising from the trust property as it arises, or have the use and enjoyment of it, such as by living in a property owned by the trustees. Such a beneficiary is also known as an income beneficiary or life tenant. There may be more than one income beneficiary, who may have either a joint tenancy or as tenants in common. The trustee must pass all of the income received, less any trustees' expenses, to the beneficiaries. For income tax purposes, the income so accruing to the income beneficiary is taxable income of the beneficiary, and taxed accordingly, unless otherwise exempted. A beneficiary who is entitled to the income of the trust for life is known as a ‘life tenant’ or as ‘having a life interest’. A beneficiary who is entitled to the trust capital is known as the ‘remainderman’ or the ‘capital beneficiary’.

A charitable trust is an irrevocable trust established for charitable purposes and, in some jurisdictions, a more specific term than "charitable organization". A charitable trust enjoys a varying degree of tax benefits in most countries. It also generates goodwill. Some important terminology in charitable trusts is the term "corpus" (Latin for "body"), which refers to the assets with which the trust is funded, and the term "donor", which is the person donating assets to a charity.

A testamentary trust (sometimes referred to as a will trust or trust under will) is a trust which arises upon the death of the testator, and which is specified in their will. A will may contain more than one testamentary trust, and may address all or any portion of the estate.

Testamentary trusts are distinguished from inter vivos trusts, which are created during the settlor's lifetime.