Final answer:
The term for a completely private language used within a family or close friends is 'intimate.' It is part of individual idiolects and reflects unique communication styles in personal relationships.
Step-by-step explanation:
The term for a completely private language that is used within a family or very close friends is intimate. Languages evolve due to various factors, and the language used in intimate settings often consists of unique words, phrases, or ways of speaking that are understood only within the particular group. This language can include in-jokes, made-up words, or a blend of different languages that reflect the group's history and relationships. An intimate language would not be considered a creole like Haitian Creole, which is a mixture of French and African languages, nor would it be a pidgin, as pidgins are simplified languages created for communication between speakers of different native languages. Intimate language is a part of personal idiolects, showing how individual identity and cultural language use shapes communication within a close-knit community.