First of all, this is not an "optional" topic. Students tell me, "Oh--I don't play reverses." This is not acceptable. It is equivalent to saying: "I don't play rebids by opener."
A "reverse" is when opener's rebid (2nd bid of the auction) meet both A & B:
A) Is in a HIGHER ranking suit than his first suit
B) Is at a HIGHER level than responder's response
So, these are reverses: