Your canon is the reference text of your business: what the AI engines should say about you, decided once, in your own words.
It is versioned. It changes rarely, and each change is a dated decision, so any page or mention can be measured against a named version of it rather than against an impression.
It is also the wording you reuse as is, everywhere, instead of rewriting the description of your business on each surface. One text, one voice, and one thing for the engines to read consistently.
It is step one of the method, and everything that follows measures against it. More on the Canon page.