To retrace one's steps or go back over a path or course. After realizing he had taken a wrong turn, he had to backtrack to find the right path.
To reverse a decision or change one's opinion. The politician had to backtrack on his previous statements after facing public criticism.
In computing or logic, to return to a previous stage in a problem-solving process when a chosen path proves unsatisfactory. If the search algorithm hits a dead end, it will backtrack to the last decision point.