Protocol most often refers to a system of rules explaining the correct conduct and procedures to be followed in a formal situation; in computer programming a protocol is a set of rules used in formatting data. Protocol can also refer to a plan for a scientific experiment or medical treatment, or to a document that describes the details of a diplomatic treaty.

// What is the proper protocol for declining a job offer?

// My doctor recommended a simplified treatment protocol for my condition.

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"Back in the UK, it's still unclear what kind of royal life, if any, lies ahead for Archie and Lilibet. While they hold their princely and princess titles, bestowed upon them following the death of Queen Elizabeth II, their day-to-day lives in Montecito are a world away from palace protocol." — Faye James, Hello Magazine, 15 July 2025

In Late Greek, the word prōtokollon referred to the first sheet of a papyrus roll bearing the date of its manufacture. In some instances, it consisted of a flyleaf that was glued to the outside of a manuscript's case and provided a description of its contents. Coming from the Greek prefix prōt- ("first") and the verb kollan ("to glue together"), prōtokollon gave us our word protocol. In its earliest uses in the 15th century, the word referred to a record of a document or transaction. By the turn of the 18th century it was being used for the original record or minutes of a diplomatic negotiation, and still later for the etiquette observed by heads of state in ceremonies and relations with other dignitaries. This sense has since extended in meaning to cover any code of proper conduct.