Ladder mate, also known as a lawnmower mate, is a checkmate pattern given with two major pieces. They can be two Queens, two Rooks, or one rook and one queen. These pieces are used to force the enemy King to one side of the board cutting off two files resulting in checkmate.
This mate pattern is one of the most common you’ll see in games. It is one of the most simple mates to give because you’re only using two pieces that cover a lot of squares. It’s also described as a clean way of ending the game because your pieces cover every square in the file they are in so the King has many squares to move to but are all covered by the Rooks or Queens.
This is a bare bones example of this pattern. When you have two Rooks, or two Queens, or a Rook and a Queen, this mate is ideal.
Black’s King is stuck in the 7th and 8th ranks by White’s Rook. White moves the Queen on the 7th rank to check Black’s King.
Black only has one file to escape to, the back rank, or 8th rank.
White then deliver’s mate with the Rook moving to the back rank.
The Queen prevents the King from escaping to the 7th rank and both files are completely covered by White.
Note: When giving this mate, remember to take it one file at a time. If White moved his Queen to the back rank first, and then moved the Rook to the 7th rank, Black would be able to escape down the board and White would have to chase the King blocking the next file and having to repeat the process. In the mean time Black could achieve a draw which would feel like a victory for Black. Black has no chance of winning in this position so if Black achieved a Draw or stalemate, White loses out on an otherwise 100% of winning the game.