D&D 5E What is the official name for the thing in parenthesis next to the creature type?

[Dracuwulf]

i.e.,

Humanoid (Elf)

What is the official dnd name for what 'Elf' is in the type above?

Descriptor? Sub-type? what?

 

[Ashardalon]

It's subtype.

 

[Fester]

Yep. And that's, like, official