Being authenticated is the technical term for being logged in. Many web apps require users to be authenticated to access content or update data. Being authenticated means that the system knows who you are.
There are several ways to be authenticated. A popular method is session-based and uses an email/password combination to authenticate users. That means an email and a password is given by the user and the system checks whether that's a valid combination that exists. If it does then they are logged in. Session-based authenticated is also called stateful authentication.
Another common approach is token-based authentication. This method is usually used when calling API endpoints. In this case, the token is issued by the system and is included in each request. The system can then block requests where a valid token isn't provided. Token-based authentication is also called stateless authentication.