A heuristic function is an arbitrary function that, given some information, returns how "good" a certain position, choice, or action might be.
A state closer to
In uninformed search strategies ( #uninformed ) we never determine which states look most promising for expansion at a given time point. We never “look-ahead” to the goal. However, we have some knowledge about the merit of states. Using a heuristic brings us to Informed Search strategies.