What is a user name and what is a display name?

A display name is what is displayed to others, whereas a username is what is used by the user. Often, the two are one and the same, but in some cases, you will use the one to sign in, but the other will be what is visible to the rest of the world, as I said earlier. Also, a display name is often used when you use an email address to sign into a service, as is the case with some social networking sites and web forums