i just figured out there is no official name for this syntax, i could be wrong:

name@example.com

it should be called an account, because that's what it represents, and that is what it always has represented, a login name and the domain it applies to (a credential would be including the password or other auth)

to be really strictly correct, it's a domain account, but that is a bit redundant

nip-05 names are a domain account, emails are a domain account, all the centralized services use these account things