I am a beginner in OpenGL, and I would like to know how to distinguish specific objects in an OpenGL game. For instance, the game world contains 3 gems of different colors, how can I know which one the user collides with exactly? P.S. At first I thought it could be picking, but no, picking is for mouse pointing
It sounds like you just want a general games development glossary like this one:
If you want to know the correct terminology for something, you'll just have to look it up. There's no 'central guide'.
Generally by the point at which you're ready to implement something in your game you'll have done enough research on it to not only know that the relevant term is but give a full etymology lesson on how that term came about :)