The ChessPawn is, by all accounts, the weakest piece on the board in a game of WesternChess, possessing only the ability to move a single square forward. In addition, it can't even capture a piece standing in its way; instead it may only capture by moving one square diagonally forward.
The use of "by all accounts" will be hereby proven inaccurate. The inability of a pawn to "move through" a blocker is not always a weakness. Offsetting a pawn chain through a blockade can sometimes lead to a draw (or win) out of a position with a clear material disadvantage. Also, ChessPawns make excellent protectors (i.e., if there is a possible series of piece trades, and you protect one of them with a pawn, said trades are no longer trades but sacrifices for your opponent). True, ChessPawns have severe mobility limitations, but they are much more powerful than many people realize. I think this misunderstanding often comes from the lack of the high level of skill needed to know exactly what to do with pawns (a level which, I might add, I am also nowhere near).--DanCicio (Sorry, I always have to defend the undderrated ChessPawn from an unprovoked attack.) (Sorry, I also couldn't avoid the nerdy chess joke.)
Around the 1600s, somebody decided that it would be a GoodIdea if the pawn could move two squares forward on its first move, so as to speed up the opening phases of the game, and thus a pawn on the second rank may move two squares forward if both squares ahead of it are unoccupied.
From this change was born the en passant rule.
En passant, French for "in passing", is when a pawn captures another pawn on an empty square. If a white pawn moves two squares on its first move and there is a black pawn that could have captured it had it only moved one square, the black pawn can capture the white pawn as if it had only moved one square (i.e. it moves diagonally forward onto the empty square that the white pawn moved over and the white pawn is removed from the board). If the black pawn does not capture immediately after the white pawn moves, the black pawn can no longer capture it en passant. (Note: All instances of "black" and "white" can be reversed.)
In WesternChess, and most derivative variants thereof, the pawn is the only unit which can promote; if it reaches the LastRank, it is replaced by a non-King, non-Pawn unit of the promoting player's choice (and color!). This is usually a ChessQueen, for obvious reasons, and thus pawn promotion is often known as "queening".
This ability is what makes ChessPawns so much fun in BugHouse and ChesSers-- although drops directly on the LastRank are verboten, drops on the seventh rank are not, and a threat to promote a pawn generally cannot be safely ignored.
The ChesSers node notes that ChessPawns are useful for protecting cannon fodder, kicking knights, and threatening to promote. They can also form an integral part of a mating net. (But not on the checkers board, which is what that particular paragraph is discussing.)