In problem solving, the term rule of thumb refers to

The term rule of thumb refers to heuristic.

A heuristic is a mental shortcut that allows people to make judgments efficiently and quickly.

The word heuristic comes from Greek find or discover.

It a an approach to problem solving that uses a practical, rational or logical method. This method may not always be correct, but it's sufficient to reach an immediate goal.

Some examples of heuristic are: the rule of thumb, an educated guess, common sense or an intuitive judgement.

The rule of thumb refers to a procedure or standard based on practical experience rather than theory.  

It refers to a solution based on practice rather than on theory.

The term rule of thumb refers to finding solutions that are more practical than theoretical.

It is a form of heuristic which can be understood as a mental shortcut. In problem-solving refers to following a path that has shown to work in the past.

It can also be understood as the act of following an easy to learn procedure or standard based on practicality rather than on theory.