The straight man of the Marx brothers.
Also in teenage cliques, the average one. Most commonly found in the most popular groups, this person is treated as an equal, but is there to provide contrast to the others greatness, while not posing a threat. For instance, the cheerleaders usually have one girl that has a "great personality" or "really pretty face" to make the others feel more beautiful. Thankfully, nerd groups tend to lack this feature/bug. Always thought it was an east coast expression but I guess its spread.
This is different from the Omega of the group and the hoverers of the group of course.