Keywords: Go term
A variation is a possible sequence of moves from a starting position. It usually refers to a sequence that is different from either the main line of a Go problem or the actual sequence played in a game.
Some tsumego books contain only three explanatory diagrams for each problem: a solution diagram, a variation diagram, and a failure diagram. In such publications, typically the solution diagram contains the main line, the variation diagram describes the most interesting variation of the solution, and the failure diagram gives a canonical wrong variation.