In some search problems we don't just care about finding a solution state that satisfies constraints, but the solution path, the way in which we got to the goal state. For example there may be a cost attached to moves. This may be an additionalconstraint, such as the maximum available time for moves on a chess clock, or may be part of an optmisation criterion, for example solving Rubik's cube in as few moves as possible.
Used in Chap. 4: page 36
Also known as solution path