A nickname for the city of Fredericksburg, Virginia. It is a reference to the fact that there is very little to do in Fredericksburg, Virginia. Quite the opposite of Las Vegas, Nevada, where there must be very much to do.
Also, it is the user name of a hugely popular member of a few internet message boards based in the Virginia area. You know that's true, don't even try to make jokes.
Is that Fredvegas? From Fredvegas? He's hugely popular.