A Heuristic is a step-by-step problem-solving procedure which usually leads to a sufficiently close approximation of the right result. Often, a Heuristic has the potential to also deliver very wrong results. Heuristics are used in scenarios where an appropiate Algorithm is either unknown or computationally infeasible, and occasionally getting bad apples is an acceptable trade-off to not solving the problem at all.

Of course, this is a heuristic, which is a fancy way of saying that it doesn't work.
--Mark-Jason Dominus

Contrast Algorithm.