what is mule
Definition of MULE. 1. a: a hybrid between a horse and a donkey; especially: the offspring of a male donkey and a mare b: a self-sterile plant whether hybrid or not c: a usually sterile hybrid. 2.: a very stubborn person. 3.edical Definition of MULE. : a hybrid between a horse and a donkey; especially: the offspring of a male donkey and a mare.