Slang — jargon (5)
I believe the answer is:
lingo
I believe this is a double definition.
'slang' is the first definition.
(lingo can mean slang or jargon)
'jargon' is the second definition.
(synonyms)
(Other definitions for lingo that I've seen before include "Johnny Foreigner speaks one" , "Parlance" , "Log in (anag.)" , "Foreign language or dialect: jargon" , "special words" .)