Also called an account name, login ID, nickname, and user ID, username or user name is the name given to a computer or computer network user. This name is commonly an abbreviation of the user's full name or alias. For example, an individual known as John Smith may be assigned the username smitj, the first four letters of the last name, followed by the first letter of the first name. The picture shown on this page shows the username as root.
Usernames allow multiple users to use the same computer or online service with their settings and files. When used on a website, a username lets you 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 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 with 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 sends you your username through e-mail. A link for this feature is usually found under or around where you enter your username and password.
Is it a username, user name, or user-name?
With an identity used with a password, "username" is used. If referring to a real 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 the username used with his password.
The Microsoft Manual of Style 4th Edition states that the user name should be two words unless describing a label in the user interface.