Canonical is an adjective that characterizes that which is in accordance with the canons, with the standards established or agreed.
Canonical has a special meaning when referring to the Roman Catholic Church, following several elements linked to the Church: canonical wine, canonical rite, canonical prayer, list of saints recognized by the church etc.
The Code of Canon Law is the set of norms (canons) that guide ecclesiastical discipline, define the administrative hierarchy, the rights and duties of the Catholic faithful, the sacraments and possible sanctions for transgression of the standards.
In Grammar and Linguistics, the grammatical structure that follows the norms defined in Grammar is designated as canonical. For example, subject + predicate is the canonical syntactic structure of the terms of a clause.
In Mathematics, the canonical form is a simple way to present some mathematical object, which can be a matrix, an equation or a formula. Regarding matrices, Jordan's canonical form is one of the best known.