The word "Pom" was used to reference British people starting in 1912. The word is a shortened version of the word "pomegranate," which over the years had become a slang name for British immigrants.
Around 1850, Australians began to refer to British settlers as "Jimmy Grants," a generic name that rhymed with "immigrant." In 1912, "Jimmy Grant" would change to "Pommy Grant," then to "pomegranate." Additionally, sometimes the slang is changed to "Pommy" instead of "Pom."
According to an incorrect myth, Pom is an acronym for "Prisoners of His Majesty" or "Permit of Migration," referring to the fact that the original settlers of Australia were convicts from Britain.