In the game of Go, a ladder (四丁, シチョウ, shichō)[1],(Chinese: 征子, romanized: zhengzi) is a basic sequence of moves in which an attacker pursues a group in atari in a zig-zag pattern across the board.
If there are no intervening stones, the group will hit the edge of the board and be captured.
Secondary double threat tactics around ladders, involving playing a stone in such a way as to break the ladder and also create some other possibility, are potentially very complex.
[4] Although ladders are one of the first techniques which human players learn, AlphaGo Zero was only able to handle them much later in its training than many other Go concepts.
[5] Other Go AI such as AlphaGo (before AlphaGo Zero) or KataGo use information about ladder outcomes as input features of their neural nets.