A more thorough explanation:

COMPELLATIVUS

Compellativus is a grammatical term used to describe a noun or pronoun that is used to address or call someone or something directly.

• "Hey, John!" - In this example, "John" is the compellativus because it is used to directly address someone.
• "Excuse me, sir." - In this example, "sir" is the compellativus because it is used to address someone directly.

The examples illustrate how the compellativus is used to directly address someone or something. It is a way of getting someone's attention or showing respect by using their name or a title.