Alternatively referred to as an account name, login ID, and user ID, username or user name is the name given to a user on a computer or computer network. This name is commonly an abbreviation of the user's full name or his or her alias. For example, an individual known as John Smith may be assigned the username of smitj, which is the first four letters of the last name followed by the first letter of the first name. In the picture shown on this page, the username is root.
Usernames allow multiple users to use the same computer or online service with their personal settings and files. When used on a website, a username enables you to maintain personal settings and identification with that website or service.
What is my username?
With most services, your username is a name you created, or that has been assigned to you. If you do not recall creating a username, (or don't remember the name you chose), try using your e-mail address as your username. If your e-mail address does not work, and you are trying to log into a service where you have an account number, try using that number.
If none of the above suggestions work, most services have a forgot username or forgot password service that can be used to send you your username through e-mail. Typically, a link for this feature is found under or around where you log in.
Is it a username, user name, or user-name?
When referring to an identity used with a password, "username" is used. If you are referring to a real name or full name, "user name" could be used. As far as "user-name," it is rarely used. In our earlier example, "John Smith" is the user name, and "smitj" is his username used with his password.
Note: The Microsoft Manual of Style 4th Edition states that the user name should be two words unless describing a label in the user interface.