The difference between Canonical form and Citation form

Canonical form as a noun (mathematics, computing):

A standard or normal presentation of a mathematical entity.

Canonical form as a noun (chemistry):

Any of a set of representations of the resonance structure of a molecule each of which contributes to the real structure; a contributing structure.

Canonical form as a noun (linguistics, rare):

Lemma, or dictionary form; a basic form of a word used as a dictionary entry.

Citation form as a noun:

The basic form of a word used as a dictionary headword.