The term problem solving means slightly different things depending on the discipline. For instance, it is a mental process in psychology and a computerized process in computer science. There are two different types of problems, ill-defined and well-defined: different approaches are used for each. Well-defined problems have specific goals and clear expected solutions, while ill-defined problems do not. Well-defined problems allow for more initial planning than ill-defined problems. Solving problems sometimes involves dealing with pragmatics, the way that context contributes to meaning, and semantics, the interpretation of the problem. The ability to understand what the goal of the problem is, and what rules could be applied, represents the key to solving the problem. Sometimes the problem requires abstract thinking or coming up with a creative solution.