Term defining a large truck or group of people that obstructs the flow of traffic, either intentionally or unintenionally. Taken from Starcraft, where Ultralisks commonly block up base entrances by accident, preventing zerglings from entering or leaving.
Doug: Dammit, this semi is being a real ultralisk.
Steve: Well, I think you'll get a shot at passing it in a second, oh wait, he moved to keep you from passing. What an ultralisk.
A large mammoth like creature from the legendary game Starcraft. When you see one eating your neighbor leave him alone.
Father: Son, why aren't you eating your SOUP??!
Son: The ultralisk's told me not to :/