In general heuristic is approach or method that don't offer 100% efficiency or exactness of result but can give you the right or enough close answer on some area of tasks. For example in a platformer game you don't need to simulate physics. You can simulate part of physics or make "physics" by predefined table (IIRC like in mario). Sometimes you don't need exact value and if error is less than particular value, you don't need to worry....
P.S Thanks for recommendations