Username (noun)

A name or nickname that a person uses on a particular computer system or website, in order to identify themselves to other users.

Origin:

Late 20th century: blend of user and name.

Examples:

1. Please enter your username and password to log in.
2. Your username must be unique and can't be changed later.
3. A username is a unique identifier that allows a user to access an account or system.
4. I forgot my username, can you help me to retrieve it?
5. Please choose a username that is easy to remember and not easily guessable.