The pawn on a2 is backwards, because it's behind the rest of the pawns in its chain, or it's the last pawn at the end of a chain, and so susceptible to attack. You could think of them as behind-pawns instead of backwards-pawns, if it makes it easier.
I have read a handful of literature on this topic online and heard lots of talk on this via youtube but I still don't get it. What the hell is a backwards pawn. Lol, please explain in simplistic terms.
Thanks in advance.