What is Postbit
 

I keep reading the term POSTBIT and I dont understand what that term means. Is there a "dictionary" of sorts for these kind of terms and what does that word really mean?
Thanks

It's the name of a template in your Admin CP. The postbit is the template you edit to change the look of your posts when you use layout with the avatars in a column above the post. The postbit_legacy template is the one when you edit when you have your avatars to the left of your posts.

Thank you! Is there a place where I can see exactly what template covers what?

There's been talk for sometime of someone making one, but I don't think it's every happened. I think the reason for that is most of the modifications you'll look to add will tell you what templates to edit, and once you start editing them, after a while you begin to get an idea of the pattern used when vB named them.