Pathfinding is all about finding a valid path from A to B, where A and B are simply states. If more than one
path exists, then we want the “best” one. When we talk about pathfinding, we generally mean finding a
path from one position to another, like on a map. It is more general than that however. The states A and B
could just as well be states of a game of chess, or more simple states describing the position of the tiles in a
9-puzzle, and then the path would consist of the steps needed to go from one state to the other. A
generally being the current state of the puzzle and B being the final solved state.
The full text is in the form of a PDF document that can be downloaded at the bottom of this page. Consider the text as a very basic introduction to the method as well as the to its uses outside the problem domain of finding a path through an ordinary "map".