Slang name for the North American Pronghorn (Antilocapra americana). So named due to it's close resemblance to a goat and it's incredible speed.
While it's difficult to measure their speed, most sources state upwards of 70 Km/h, and they're known to be the second fastest land animal, second only to the cheetah, but able to sustain higher speeds for longer distances than the cheetah.
Oh, Crap! We're going to hit that speed goat. Duck! Why do they hang out near the highway?
I've given up hunting speed goats because they taste like a cross between a Slim Jim and sagebrush.