Informal address is a term used to describe a type of address that is not formal or official. It is often used in casual conversations between friends and family. The two crossword solutions for this term are 'KIDDO' (5 letters) and 'MAC' (3 letters). KIDDO is an affectionate term used to refer to someone younger than you, such as a child or a close friend. MAC is a shortened form of the name 'Mackenzie' which is often used as a nickname.