Informal
Part of speech: adjective
Definition: Not formal or ceremonious; casual. Not in accord with the usual regulations; unofficial. Suited for everyday use. Reflecting everyday, non-ceremonious usage. Not organized; not structured or planned.
Example sentence: The Science Coalition, which grew out of an initial concept at Harvard and at MIT, has now grown to an informal group of about 60 research universities.
Unofficial
Part of speech: adjective
Definition: not officially establishednot acting with official authority(of a drug) not listed in a national pharmacopeia etc