"Canon" refers to those story elements which were created by Disney or official Disney-endorsed sources, such as the three Lion King movies, Disney-produced storybooks, comics, and so on. This is as opposed to story elements created by fans, the most well-known and widely accepted of which can be referred to as "fanon". A fuller definition of "canon" in a general sense (as applied to any fictional universe) can be found here.

Some useful lists: