Is a pawn still backward if other pieces can defend it? What exactly is a backward pawn?  Is it a pawn that can't be defended by its own pawns or if other pieces can defend it, is it still considered backwards.

As an example, in the following is e5 and d4 backwards`.

[FEN ""]
1. e4 e5 2.Nf3 Nc6 3.Bb5 d6 4. d4


Also, if a pawn is backwards if it can't be defended by its neighboring pawns, then doesn't this mean that every pawn starts off as backwards in the initial position of the game.
According to Wikipedia:


  "...it is a pawn that is behind a pawn of the same colour on an adjacent file and that cannot be advanced without loss of material, usually the backward pawn itself. In the diagram, the black pawn on the c6-square is backward."





  "Pieces can become weak when they are devoted to protecting a backward pawn, since their obligation to defend the pawn keeps them from being deployed for other uses."


So it is still a backward pawn if it is protected by another piece. Perhaps it is protected, but now it has become a burden on a more valuable piece.

The backward pawn creates an obligation upon (and therefore decreases the value of) whatever piece is defending it. There is a penalty if the piece defending the backward pawn moves elsewhere (loss of the pawn).