What is the difference between a prawn and a shrimp?

What is the difference between a prawn and a shrimp?

With prawns the first three of the five pairs of legs on the body have small pincers, while in shrimps only two pairs are claw-like. In some shrimps one or other of the first two pairs of legs is bigger than the other whereas in prawns all the legs are similar lengths. A shrimp in the USA is a prawn in Australia!