What is A* pathfinding?

The A* pathfinding algorithm is a development of Dijkstra’s shortest path.  Unlike Dijkstra’s algorithm, A* finds the shortest path between two vertices on a weighted graph using heuristics.  It performs better than Dijkstra’s algorithm because not every vertex is considered. Instead, only the most optimal path is followed to the goal. 

Known as a best-first search algorithm, with A* pathfinding a heuristic estimates the cost of the path between the next vertex and the goal.  It then follows this path.  It is important that the heuristic does not over-estimate the cost, thereby choosing an incorrect vertex to move to next.  The vertices being considered are referred to as “the fringe”. 

The usefulness of the A* algorithm is determined by the suitability of the heuristic.