Canon (one “n”) refers to a collection of rules or texts that are considered to be authoritative. Shakespeare and Chaucer are part of the canon of Western literature, so you might read their work in an English class.
A canon can also be a body of work, like the Shakespeare canon, which includes all of the Bard's plays and poems. These days, many schools and colleges include more diverse and underrepresented authors in literature classes and encourage students to read works not included in the standard literary canon. The literary canon can change with time, and so can the cultural canon. Don't confuse this word with cannon with two n's, the big gun that shoots bowling-size balls at the enemy.