not formal; not following official or established rules, methods, etc.
(of clothes, behaviour, etc.) suitable for ordinary everyday situations but not for official occasions
"conservative people unaccustomed to informal dress"
"an informal free-and-easy manner"
"an informal gathering of friends"
"an informal agreement"
"a loose organization of the local farmers"
"had a cozy chat"
"a relaxed informal manner"
"an intimate cocktail lounge"
"the small room was cozy and intimate"
An informal alliance was formed between the Barbers' Company and the Fellowship of Surgeons.
出自： M. Rule
This garden is..very informal I don't think you could find a straight edge anywhere!