Meaning of INFORMAL in English

INFORMAL

/ ɪnˈfɔːml; NAmE ɪnˈfɔːrml/ adjective

1.

relaxed and friendly; not following strict rules of how to behave or do sth :

an informal atmosphere

an informal arrangement / meeting / visit

Discussions are held on an informal basis within the department.

2.

( of clothes ) suitable for wearing at home or when relaxing rather than for a special or an official occasion

SYN casual

OPP formal

3.

( of language ) suitable for normal conversation and writing to friends rather than for serious speech and letters :

an informal expression

—compare formal , slang

►  in·for·mal·ity / ˌɪnfɔːˈmæləti; NAmE -fɔːrˈm-/ noun [ U ]

►  in·for·mal·ly / ɪnˈfɔːməli; NAmE -ˈfɔːrm-/ adverb :

They told me informally (= not officially) that I had got the job.

to dress informally

Oxford Advanced Learner's English Dictionary.      Оксфордский английский словарь для изучающик язык на продвинутом уровне.