A username is a unique combination of characters that identifies a specific user.
Such as, letters of the alphabet or numbers or alphabet and numbers, that identifies a specific user. In an Internet e-mail address, an @ (pronounced at) symbol separates the user name from the domain name. Your service provider supplies the domain name. A possible e-mail address for Kiley Barnhill would be firstname.lastname@example.org, which would be read as follows: K Barnhill at e site dot com. Most e-mail programs allow you to create an address book, or contacts folder, which contains a list of names and e-mail addresses.
Username is not valid. Enter a valid username which contains only letters and numbers and only one underscore.