In some search problems we don't just care about finding a solution state that satsifies constraints, but the soltion 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 andditionalconstraint, 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 as possible moves.
Used on Chap. 4: page 53
Also known as solution path