When the calibre of nerdy is matched by the size of butt, commonly seen in cargo pants. Often easily identifies a nerd by the size of butt in higher worn pants.
A supremely high and perfectly muscular ass on what would otherwise be a total nerd, thereby doubling the sex appeal factor for women. In other men, the nerdbutt demands a solid on the spotsucker punch.
Jen: "Ugh! All Drew does is play WoW and design jersey logos for high schoolfrisbee teams... But he has the greatest ass I've ever seen."
Gabe: "Nerdbutt!"