This seems to be an attempt to decorate the definition of a term. Similar typography is used earlier for "default constructor". The word "constructor" is not itself italicized, since constructors as a whole aren't what's being defined; rather, only one particlular kind of constructor is being defined. Similarly, there are many assignment operators, but the sentence in question only defines the specific copy assignment.

However, this rule does not seem to have been applied consistently. If it were, we should also italicize:

• copy constructor
• move constructor
• move assignment operator

Also, in general, we define entire phrases, not just one part of a phrase. So, we should actually italicize all of "copy constructor" where we define it.

Editorial meeting consensus: Italicize the entire term-of-art we're defining.

Ask CWG to permit deleting "user-declared" in the definitions.