[temp.spec] Convert description of "specialization" to a proper definition

Author: sdkrystian

source/templates.tex

@@ -5805,8 +5805,9 @@
 An instantiated template specialization can be either implicitly
 instantiated\iref{temp.inst} for a given argument list or be explicitly
 instantiated\iref{temp.explicit}.
-A specialization is a class, variable, function, or class member that is either
-instantiated or explicitly specialized\iref{temp.expl.spec}.
+A \defn{specialization} is a class, variable, function, or class member that is either
+instantiated\iref{temp.inst} from a templated entity or is an
+explicit specialization\iref{temp.expl.spec} of a templated entity.
 
 \pnum
 For a given template and a given set of