Lucena position
Also called Building a bridge.
The key winning position in rook endings: rook, king and pawn on the seventh against a rook, with the defending king cut off.
The stronger side’s king stands on the queening square in front of its pawn, and the defending king is cut off by at least one file. Without that cut-off it is often a draw. The stronger side shelters its king from checks by using its own rook as a bridge, then queens the pawn. Knowing it, and the Philidor position, covers most rook and pawn against rook endings.