A pawn chain is a structure in which two or more pawns of the same side are lined up diagonally, each one protecting the pawn directly in front of it. This formation creates a solid ridge that splits the board into two zones and has a deep influence on the strategy of both sides.
The chain consists of a head (the most advanced pawn), one or more intermediate pawns, and a base (the rearmost pawn, which receives no protection from the rest of the chain). The base is the chain’s Achilles' heel: because no friendly pawn guards it, it is the natural target for the opponent. If the base is destroyed, the entire structure loses its coherence. The head, for its part, serves as the spearhead of its owner’s spatial ambitions.
In practice, recognising a pawn chain gives you a clear plan. If you own the chain, advance it to gain space and restrict your opponent’s pieces. If you are facing one, attack its base with your own pawns to break it apart and open files for your pieces.