Mental shortcuts for solving problems quickly.
Heuristics are mental shortcuts that allows people to solve problems and make judgments quickly and efficiently. These rule-of-thumb strategies shorten decision-making time and allow people to function without constantly stopping to think about their next course of action.
Heuristics are not a good thing, nor a bad thing. They have good and bad qualities. They are a significant contributor to Noise and Bias Index.
The SEBoK defines heuristics as:
Principles learnt from practical experience that yet lack a scientific understanding as to the explanation of “why”. (SEBoK pg 92)