A wider approach to the study of human task-oriented behaviour than epistemology, logic, or scientific method, as it also includes such things as motivation, cultural influences, tradition, personality, context, etc.
A heuristic is a problem-solving strategy used when no step-by-step procedure is applicable. It can also be a set of instructions for searching out an unknown goal by incremental exploration, to some unknown criterion, for example by following the instruction to make every step upward, a person can reach the top of a hill even in a fog and without knowing the location or height of the top.
The solution to a problem changes the nature of the problem.