The ladder mate is an endgame checkmate pattern in which two rooks (or a rook and a queen) progressively drive the opposing king to the edge of the board by stripping away one rank or file at a time, until checkmate is delivered.
The name comes from the visual shape traced by the successive moves: the two pieces advance in alternation, like the rungs of a ladder, pushing the king back one rank at a time. For example, with rooks on h1 and a2 against a king on e5, the rook on a2 checks on a5, the king retreats to e4, then the rook on h1 checks on h4, the king retreats to e3, and so on until the edge. The king has no escape because the second rook always controls the adjacent rank.
In practice, watch out for stalemate: if the opposing king is forced to the edge with no available square AND is not in check, the game is an immediate draw. Before delivering the final blow, always verify that the king still has at least one square to move to — that will be the square where you deliver checkmate.