Extinct language

A language is defined as "extinct" when no one is using it. If someone is using a language, but there are no beings alive who learned it as children, then it is technically classified as a "dead" language.

Conlangs
Some fictlangs are canonically classified as "extinct", but the vast majority of conlangs are, for lack of a better word, doomed to extinction, due to the fact that they hold no intrinsic value. This doesn't mean that people shouldn't make them; it just means that you shouldn't worry about whether or not people will speak your language after you die. If you worry about that now, as you make it, they may very well not.