A Fediverse ID is an identifier that conceptually is usually used to point to a person, but also can be conceptually used to point to an application, a group, a organization, a service, or any types of entities.
Here are some sample Fediverse IDs:
A Fediverse ID looks similar to an e-mail address.
The main superficial difference being that a Fediverse ID starts with an at sign (“@”) (Unicode character U+0040), but an e-mail address does not.