Problem refers to a situation, condition, or issue that is unresolved or undesired. Usually, the nature of a problem is such that an answer or solution is needed. In such cases, problem solving is used to understand important aspects of the problem so that an answer or solution can be found.

Problems occur in different forms, and can exist in different domains. Examples are provided below.

• In mathematics, a problem is a question about mathematical objects and structures requiring explanation and proof. These questions range from very specific ("What are the real solutions of x² + 1 = 0?") to quite general ("Why do these numbers appear in apparently different situations? Formulate and prove a conjecture.")
• In society, a problem can refer to particular social issues, which if solved would yield social benefits, such as increased harmony or productivity, and conversely diminished hostility and disruption.
• In business, a problem is a difference between actual conditions and those that are required or desired. Often, the causes of a problem are not known, in which case root cause analysis is employed to find the causes and identify corrective actions.