/ 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