What you’re referring to is known more technically as "vocative case". If you look up "direct address" on Wikipedia you’ll be redirected.

From there, as a Latinate word, the translation is pretty direct: le vocatif.

You could also "reverse engineer" a more word-for-word translation for the original term by using that page’s French description of the term:

l’interpellation directe ou l’invocation d’une personne

(The trick I often use for such things is to look up the English on Wikipedia and then use the language switcher / list of other languages to find the same article on French Wikipedia. This method seems to be pretty reliable for finding standard equivalents for technical jargon.)