Lucena position
The Lucena position is a winning rook endgame with a pawn on the seventh rank, decided by building a bridge for the king.
Your king is in front of the pawn on the seventh, their king is cut off, and their rook checks from the side or the rear. You cannot just step out: the checks never stop until you block one.
The bridge is a rook lift to the fourth rank. The king leaves the pawn, weathers a few checks, then hides behind its own rook so the pawn can promote.
If the defender’s king is in front of the pawn instead, you are not in Lucena — you may be in Philidor, which is a draw. The difference is whose king stands on the promotion file.