A heuristic is a rule or method that helps you solve problems faster than you would if you did all the computing. It sounds fancy, but you might know a heuristic as a "rule of thumb."
Derived from a Greek word that means "to discover," heuristic describes a rule or a method that comes from experience and helps you think through things, like the process of elimination, or the process of trial and error. You can think of a heuristic as a shortcut. Besides finding it in philosophy books, if you are interested in computing, you'll find references to heuristic programming. You can use it as a noun or as an adjective.