In the back of your book...
Today we challenge you to create a glossary for your character. Definitions of those 'in jokes' , unfamiliar terms, people places and things that matter... things the casual reader might need help in understanding in order to get the most out of your character's story.
(This is an oldie but goody from a few years back - if you already created a glossary for your character then, now's a good time to update it.)