Back in olden times when messages were sent by telegram, charged by the word, and also extremely slow to send by morse code, there were an extensive range of code words used for all sorts.
The old GWR named all their internal user engineering wagon types after fish, for some reason (maybe Grierson, longstanding Chief Civil Engineer, was a fisherman), so you had to know your Catfish from your Dogfish - the former was a 20 ton ballast hopper, the latter a larger 25 tonner. Universally used in messages, these names were also painted on the sides of the wagon.