Insider language (5)
(Other definitions for jargon that I've seen before include "Bandied words, possibly" , "Language specific to an activity" , "Insider idiom" , "Argot" , "Pidgin" .)
(Other definitions for argot that I've seen before include "Kind of slang" , "Language of a particular group" , "Criminal jargon" , "Talk of thieves" , "Specialised language" .)