screen name vs. display name

So I just discovered (probably a new feature) that if you want to look for someone on CC you can enter the person's screen name or the display name. What is the difference?

Some people use different names -- the Screen Name is the name that is below your picture or avatar (Plume for you), the Display Name may be the same (Plume again for you), may be non-existent, or may be completely different from the screen name.

thanks. I learned something new :-)