The word calf can mean either a baby cow or bull, or the area of the back of your leg between your ankle and knee.
Cattle are not the only animals whose babies are called calves. You can use the word to mean a baby whale, baby elephant, camel, bison, elk, giraffe, gnu, hippopotamus, moose, ox, reindeer, rhinoceros, and yak. If a large piece of ice breaks off of a glacier or iceberg, well that's a calf too! If you want to strengthen your calves, doing heel raises while holding a calf is an interesting way to go about it.