The simplest pawn chain is two or three pawns diagonally connected to each other. More complex pawn chains are possible. You can have a single base pawn with diagonal pawns going out in both directions. Or you can have pawn chains that go up and down, with multiple “base pawns” in the chain. The base pawn of a pawn chain is a weakness, as it is not protected by any of its other pawns. So “attack the base of the pawn chain” is a well-known strategy to attack and undermine a pawn chain.
Closed positions often have pawn chains where both player’s pawns have become blocked by the other pawn chain. In such positions, there are usually two sets of pawn chains, on opposite color squares.
Related Chess Tactics
Read more about these related chess strategies: