It seems that when we refer to a particular class, function, etc. generated from a template, we generally say such a thing is a "specialization" but not "instantiation", and the word "instantiation" generally refers to the process of template instantiation or explicit instantiation declaration/definition.

However, there're many occurrences of "instantiation" (mostly in the library wording?) actually meaning "specialization". E.g. in [namespace.std]/6:

[...] or an instantiation of a standard library function template. [...]

For the core wording, there's a questionable term "current instantiation" in [temp.dep.type]/1. It seems that a current instantiation is always a class, so it's possibly unconventional to name the term "current instantiation" but not "current specialization".