The glossary is a nice place for the user to read and understand what a particular word or phrase means in just a sentence or two. These terms can be referred to easily from anywhere in the docs using (for example):

:term:`Vertex`

which will link to the corresponding entry on the glossary page.

It'd be nice for someone to think up a few common terms to add to the list (e.g. Face, Key Frame, Edge Loop, Manifold...) and complete the existing TODO items there.

It is not meant to be a place for lengthy explanations - if more than a few paragraphs are needed it would be better to create a new document in the appropriate place and link to that. For example:

Key Frame
   A frame which defines the starting or ending points of a transition. See more :doc:`here </animation/introduction>`