A problem is an issue or obstacle which makes it difficult to achieve a desired goal, objective or purpose. It refers to a situation, condition, or issue that is yet unresolved. In a broad sense, a problem exists when an individual becomes aware of a significant difference between what is potential and actual.
Every theoretical problem asks for an answer or solution. Trying to find a solution to a problem is known as problem solving. That is, a problem is a gap between an actual and desired situation. The time it takes to solve a problem is a way of measuring complexity. Many problems have no discovered solution and are therefore classified as an open problem.