1) An act or instance of extending; the state of being extended.
2) Physics: That property of a body by which it occupies space.
3) Math.: A field F is said to be an extension of a field
K if K is a subfield of F.
4) Logic: The sum of all individuals or objects to which
the comprehension of a term is applied. For example, the extension of the
term "dog" is the set of all (past, present and future) dogs in the world.
Verbal noun of → extend.