The term 'Idiomatic Vocabulary' refers to a type of language that is used in everyday conversation and includes words, phrases, and expressions that are specific to a certain culture or region. The crossword solution for this term is 'ARGOT, ' which is defined as a specialized vocabulary used by a particular group of people, such as criminals or members of a profession. ARGOT is often used to create an exclusive sense of identity among its users, and it can also be used to keep outsiders from understanding the conversation.