Heuristic describes an approach to problem solving which emphasises practical experience rather than theoretical explanations.
It is sometimes known as the use of 'rules of thumb'.
Heuristics may include very simple numbers, which capture the essence of a more complex situation.
Executing the solution then includes focus on the simple number and improving it, mindful that it is a simplification, without allowing the complexity of the underlying situation to hamper progress.
Other heuristics may be entirely qualitative.