Mirrored from Sudopedia, the Free Sudoku Reference Guide
A backtracking algorithm solves a Sudoku by trying to place a digit into a cell, then working out the consequences and placing other digits until the program either hits a dead end, or finds a solution. If a dead end is reached, the algorithm then removes the placed digits and tries the alternatives. This process continues until all alternatives have been tried.
Another name for backtracking is depth-first search.