The main difference between the two is their reproductive difference. Bulls are known as male bovines. They will have the ability to mate and reproduce with others because their testicles have not been removed. A steer, on the other hand, is also known as a male bovine. The main difference is that the testicles of the steer have already been removed.
This means that it will not have the ability to reproduce anymore even if it mates. There are some bovines that are castrated long before they reach the age of maturity. No matter what their other differences are, it is best to remember to know how to be safe when these animals are around.