Ulkopuoli

Ulkopuoli is a Finnish term meaning the exterior or outside part of something. It denotes the side or region oriented away from the interior or from a given reference point. The concept is commonly used in everyday language as well as in technical contexts to describe the outer surface, façade, or external aspects of objects, buildings, or materials. Its opposite is sisäpuoli, or the inside.

The word derives from ulko- meaning outside and puoli meaning side. In ordinary use, ulkopuoli refers to what is on the exterior or external face of an object, contrasting with the inner side or inner structure.

In mathematics, specifically in topology, ulkopuoli refers to the exterior of a subset A in a topological space X. It is defined as the interior of the complement of A, i.e., ext(A) = int(X \ A). Equivalently, ext(A) = X \ cl(A). The exterior consists of points that have a neighborhood disjoint from A and does not include points of A or its boundary. For example, the exterior of a disk in the plane is all points outside the disk.

Outside uses of the term extend to design, architecture, and everyday description of objects. The ulkopuoli of a building, for instance, describes its outer surfaces and façades, while in clothing or packaging the term can denote external surfaces or exposure.

See also: sisäpuoli, reuna, raja, boundary.