From Sudopedia, the free Sudoku reference guide
Backtrack
From Sudopedia
Return to an earlier position in the solving path, after a contradiction or a dead end has been reached.
Backtracking is mainly used by Sudoku computer programs to determine the validity of a Sudoku by establishing that it has a unique solution.
With the aid of computer programs, human players can also backtrack using the Undo functionality. Players only need to backtrack after a guess or when using Trial & Error.
A popular metaphor for backtracking is Ariadne's Thread.
