Instantiation is obviously used a lot, but we never specify what the process entails. The english definition is not sufficient to describe it, so it should be defined.

Perhaps something like:

Instantiation of a templated entity is the process of generating a specialization through substituting template arguments in for their respective template parameters. During the instantiation of the definition of a specialization, if the substitution results in an invalid type or expression, the program is ill-formed.

This isn't a full definition by any means, but certainly a start. The second sentence sounds a little iffy.