Weak pawns or squares are pawns or squares that cannot be protected by another pawn. They can be protected by another piece but if that piece moves or is traded off it is weak.
Beginner asks about weak squares

In case you weren't aware of it, IM David Pruess has a chess mentor course on weak color complexes that goes into this.
http://www.chess.com/chessmentor/view_course?id=339
I believe weak squares are squares that are not protected by pawns. But would a square still be considered weak if it's protected by a piece instead of a pawn? What would be the difference? I'm taking lessons on this site and trying to learn to play well. Thank You.