What does 'canonical' mean? What does 'canonical' mean? 
e.g. 'write IIR or FIR in canonical form'

I get the gist of it but maybe someone here has a precise definition. In a non-DSP context it would mean something like 'strictly by the book', and perhaps in a DSP context this would mean 'without considering implementation issues'. Is this true?
A canonical implementation of a digital filter has the minimum number of delay elements. The same filter cannot be implemented with less memory. Since memory is often not the only concern, a canonical implementation is not necessarily always the best implementation on a given platform.