Canon can mean:

• A rule adopted by an ecumenical council of the Catholic or Eastern Orthodox churches. From the Greek kanon, for rule or measure. See canon law.

• The central Eucharistic prayer of the Roman Catholic Mass, containing the narrative of Jesus's institution of the Eucharist.

• An Eastern Orthodox hymn consisting of eight or nine odes selected mainly from the Old Testament interspersed with verses based on their respective themes. See Canon (hymnography) .

• A list of books accepted by an ecclesiastic communion as authoritative or divinely inspired. The term was originally Christian, referring to books declared divinely inspired by the canons of Church councils. The term has however come to be extended to other religions as well with compound scriptures, thus one can speak for instance of the Pali canon in Buddhism. See Biblical canon for a discussion of the Jewish and Christian canons. See also Taoist canon.

• The Western canon, the body of literature and art which is considered to define Western civilization by widespread consensus. These were the works with which an educated person was expected to be familiar. Increasingly after ca 1970 the idea that any such canon might exist came under attack and was stigmatized as elitist and academic. Those who defended a canon pointed out that the elite canon was generally available to all and was therefore not elitist, and that the word "academic" was merely negative code for "educated". The particularly American controversy was a skirmish in the wider "culture wars".

• In fiction, canon is the officially authorized interpretation of characters and events. It is also sometimes described as "part of a fictional universe which has inarguable validity within". In fandom, the term is often used to distinguish between "canonical" accounts (i.e. those authorized by the copyright holder) and those of fanfiction, sometimes called fanon. In serial fiction, new material can contradict earlier material (a practice known as retconning), in which case the new material becomes canon. Publishers, especially in mainstream comic books, sometimes release "what-if" stories featuring non-canonical interpretations of their characters.

• In music, a Canon is a contrapuntal composition that employs a melody with one or more imitations of the melody played after a given duration (e.g. quarter rest, one measure, etc.). The initial melody is called the leader, while the imitative melody is called the follower which is played in a different voice. The follower must be created from the leader by being either an exact replication of the rhythms and intervals of the leader, or by one of a number of other transformations. The simplest and most familiar examples are rounds such as "Row, Row, Row Your Boat".

• Canon Inc., a Japanese corporation that specialises in imaging and optical products.

• Canon, a Christian priest who is specifically attached to a cathedral and has responsibility for some aspect of its running.

• A member of certain Roman Catholic religious orders.

• A set of conventions prescribed as the proper way to paint an icon or a fresco.

• A commune of Calvados which formed into the Mézidon-Canon on September 1, 1972

• For uses of the adjective, see canonical.
• The homophonic term cannon refers to a type of weapon.