Q: What do you call a cow with no legs?
A: Ground Beef!
Explanation: Beef is a type of meat that comes from cows, cattle. When this meat is put through a grinder it is called ground beef. Ground beef is the type of meat that is found in hamburgers and other dishes.
This joke is funny because it plays with the word ground. Ground is the land you stand on when you are outside. Ground is also the past tense of the verb grind, to reduce something to small particles.
If a cow has no legs it would be on the ground, therefore, ground beef.