Learner's definition of INFORMAL
[more informal; most informal]
: not formal: such asa : having a friendly and relaxed quality
b : suited for ordinary use when you are relaxing
an informal party
We had an informal meeting over lunch.
an informal conversation
an informal writing style
He has an informal manner that puts people at ease.
c of language : relaxed in tone: not suited for serious or official speech and writing
an informal dining area
d : done in a way that is not especially careful or scientific
He spoke to them in informal Spanish/English.
The term is common in informal contexts.
an informal word