The term canon derives from the Greek κανών (kanon), meaning "rule", and thence via Latin and Old French into English. The concept in English usage is very broad: in a general sense it refers to being one (adjectival) or a group (noun) of official, authentic or approved rules or laws, particularly ecclesiastical; or group of official, authentic, or approved literary or artistic works, such as the literature of a particular author, of a particular genre, or a particular group of religious scriptural texts; or similarly, one or a body of rules, principles, or standards accepted as axiomatic and universally binding in a religion, or a field of study or art.

This principle of grouping has led to more specific uses of the word in different contexts, such as the Biblical canon (which a particular religious community regards as authoritative) and thence to literary canons (of a particular "body of literature in a particular language, or from a particular culture, period, genre").

W.C Sayers (1915–1916) established a system of canons of library classification.

S. R. Ranganathan developed a theory of facet analysis, which he presented as a detailed series of 46 canons, 13 postulates and 22 principles.

There is also the concept of the canons of rhetoric, including five key principles that, when grouped together, are the principles set for giving speeches.