Extension

Broadly, extension is the act of extending, lengthening, stretching, or enlarging something's scope, such as extending your arm to catch a ball. Additionally, in computer parlance an extension can be an additional feature that broadens the use of an application or program. In semantics and language extension can refer to the broad set of things that a concept or word can apply to.

For example, the extension of the word cat would include every cat in history, from Garfield to your pet house cat.