Mathematics
Logic or set theory
* Axiom of extensionality * Extensible cardinal * Extension (model theory) * Extension (proof theory) * Extension (predicate logic), the set of tuples of values that satisfy the predicate * Extension (semantics), the set of things to which a property applies * Extension (simplicial set) * Extension by definitions * Extensional definition, a definition that enumerates every individual a term applies to * ExtensionalityOther uses
* Extension of a function, defined on a larger domain * Extension of a polyhedron, in geometry * Extension of a line segment (finite) into an infinite line (e.g., extended base) * Exterior algebra, Grassmann's theory of extension, in geometry * Field extension, in Galois theory * Group extension, in abstract algebra and homological algebra * Homotopy extension property, in topology * Kolmogorov extension theorem, in probability theory * Linear extension, in order theory * Sheaf extension, in algebraic geometry * Tietze extension theorem, in topology * Whitney extension theorem, in differential geometryMusic
* Extension (music), notes that fit outside the standard range * Extended (Solar Fields album), ''Extended'' (Solar Fields album), 2005 * Extension (George Braith album), ''Extension'' (George Braith album), 1964 * Extension (Clare Fischer album), ''Extension'' (Clare Fischer album), 1963 * Extensions (Ahmad Jamal album), ''Extensions'' (Ahmad Jamal album), 1965 * ''Extensions'', a 1969 album by Mystic Moods Orchestra * Extensions (McCoy Tyner album), ''Extensions'' (McCoy Tyner album), 1970 * Extensions (Dave Holland album), ''Extensions'' (Dave Holland album), 1988 * Extensions (The Manhattan Transfer album), ''Extensions'' (The Manhattan Transfer album), 1979 * Extension (The Extended Mixes), 2023 album reissue by Kylie MinoguePlaces
* Extension, British Columbia, a village near Regional District of Nanaimo, British Columbia, Canada * Extension, Louisiana, unincorporated community, United StatesScience
* Extension (geology), relating to the pulling apart of the Earth's crust and lithosphere * Extension (anatomy), a movement at a joint that increases the angle between the two ends of the joint; the opposite of flexion * Extension locus, the gene locus of Melanocortin 1 receptorOther uses
* Agricultural Extension * Browser extension, a small software module for customizing a web browser * Renovation, Building extension * Continuing education, or extension school, a school for continuing education * Cooperative State Research, Education, and Extension Service, a former division of the U.S. Department of Agriculture * Extension (metaphysics), the property of stretching out or taking up space * Extension (telephone), telephone line attached to a main line or to a PBX or Centrex system * Extension cord, power cable with a plug on one end and one or more sockets on the other end * Eyelash extensions, material applied to eyelashes * Hair extensions, strands of hair added to existing hair * Extension, the building of community capacity by outsiders, for instance agricultural extension * Filename extension, for computer file systemsSee also
* Extensive (disambiguation) {{Disambiguation