In comic book terminology, these "guest star" roles are common enough that they are not considered crossovers.

In comic book terminology, an origin story is an account or back-story revealing how a character or team gained their superpowers and/or the circumstances under which they became superheroes or supervillains.

The Palestinian terminology guide is the book Terminology in Media, Culture and Politics, an instructional book released by the Palestinian Authority Ministry of Information advising terminology to be used when describing the Israeli-Palestinian conflict.