A* is a set of steps (an algorithm) that computers can use to figure out how to get somewhere fast between two places. If you have a list of locations, and how hard it is to get from one straight to the other, using A* can quickly tell you the fastest way. It's related to Dijkstra's algorithm, but makes smart guesses so that it doesn't spend as long trying slow ways. It's a good series of steps if you only want the path between two places. If you're going to ask for many paths from the same map, then there are faster ways, that find all the answers at once, like the Floyd–Warshall algorithm. A* will not work if you want to visit several places on one trip (the Travelling salesman problem).