Meaning of INFORMAL in English
[adjective] - (of situations) not formal or official or (of clothing, behaviour, speech) suitable when you are with friends and family but not for official occasionsThe two groups agreed to hold an informal meeting.He's the ideal sort of teacher - direct, friendly and informal.The famous 1969 TV documentary took an informal approach to the Royal Family.Journalists often pick up information in informal situations such as in bars and clubs.'Hi' is an informal way of greeting people.Their dinner parties are always quite informal affairs.
Cambridge English vocab. Кембриджский английский словарь. 2012