internal

Internal is an adjective used to describe something located inside or occurring within the boundaries of a person, object, system, or organization. The term derives from Latin internus, meaning within.

In biology and medicine, internal refers to structures inside the body, such as internal organs or viscera. The phrase internal medicine denotes a medical specialty focused on diagnosing and treating adult diseases non-surgically.

In technology and engineering, internal describes components housed within a device or system, such as internal memory or internal storage, and internal interfaces. The expression internal combustion engine refers to engines where combustion occurs inside the cylinders.

In business and governance, internal is used for processes and matters conducted within an organization, such as internal controls, internal audits, and internal communications. Internal affairs generally concern matters within a government or organization rather than external relations.

In philosophy and social sciences, internal can distinguish internalist positions that emphasize internal factors—such as beliefs or justifications—from external influences. In research, internal validity concerns whether a study reliably demonstrates causal relationships within its design.