Cockney rhyming slang is a form of English slang which originated in the East End of London . Many of its expressions have passed into common language, and the creation of new ones is no longer restricted to Cockneys. Up until the late 20th Century, rhyming slang was also common in Australian slang, probably due to the formative influence of cockney on Australian English.

It developed as a way of obscuring the meaning of sentences to those who did not understand the slang , though it remains a matter of speculation whether this was a linguistic accident, or whether it was developed intentionally to assist criminals or to maintain a particular community.