Inner

Inner is an adjective and noun describing something located inside or beneath the surface, as opposed to outer. When used to describe objects, it designates the interior or inner part, such as the inner layer of the earth or the inner workings of a mechanism. In everyday language, the term often refers to less visible aspects of experience or structure, such as inner life or inner feelings, and to abstract concepts like inner truth or inner self in psychology and philosophy.

In philosophy and psychology, the phrase inner life denotes mental states, thoughts, and emotions that are not immediately outwardly observable. The idea of a coherent inner self has been central to theories of identity, consciousness, and personal development, though it remains debated.

In mathematics and geometry, inner has several technical senses. The inner product is a function that assigns a scalar to a pair of vectors, enabling measurement of lengths and angles in vector spaces; spaces equipped with an inner product are called inner product spaces. In geometry, the inner radius (or incircle radius) refers to the radius of the largest circle contained within a polygon or shape.

In computer science, inner can describe constructs that exist within another construct. An inner class in languages such as Java is defined within the scope of an outer class, allowing the inner class to access members of the outer class. The term is also used to describe inner loops—loops nested inside another loop.