Polari
This was a coded slang used by gay men in the United Kingdom in the early 20th century, when homosexuality was still considered illegal. It allowed gay men to discuss their experiences without people from outside the community being aware of the content of the discussion.
It comes from the Italian “parlere,” which means to speak.
Why I Looked It Up
I ran into a news article called “Polari: The code language gay men used to survive.”