"Head Canon" refers to the creation of an alternate universe of fictional characters that exists only in your head. Sometimes this hews close to the original work of fiction (for example, instead of the Emperor dying at the end of Jedi, in my "head canon", he lives), or sometimes is dramatically different.
Such as the wedding of Mrs. Doubtifre and Boba Fett, officiated by Batman.
Who knows. Just roll with it - it's the Internet, Danny.