Technical term in logic and semantics referring to the set of all things a concept applies to. Contrasts with 内包 (intension/connotation).
「犬」の外延には、チワワもセントバーナードも含まれる。
The extension of 'dog' includes both Chihuahuas and Saint Bernards.
外延と内包の区別は、意味論の基本です。
The distinction between extension and intension is fundamental in semantics.
In logic, 内包 is a concept's defining content (intension), while 外延 is the range of things the concept applies to (extension).
A Sino-Japanese compound of 外 (outside, external) and 延 (extend, stretch), likely coined as a translation of the Western logical term 'extension'.