1.Definition: having or fostering a warm or friendly and informal atmosphere

"A relaxed informal manner"

Related Adjective(s):cozy, intimate

2.Definition: not formal

"Conservative people unaccustomed to informal dress", "An informal free-and-easy manner", "An informal gathering of friends"

3.Definition: not officially recognized or controlled

"An informal agreement"

Related Adjective(s):loose

4.Definition: used of spoken and written language