Women's Liberation is a broad-based but informal popular movement.
The school uniform is convenient because it can be worn for both informal and formal occasions.
In those days, or at any rate in Cambridge, laboratory life was rather informal.
Once you have reached informal agreement, you should enter into a contract with the other party.
Today's party is informal.
It's quite an informal meeting.
Japanese speakers of English often have difficulty in dealing with informal conversation, such as at parties or in small informal groups.
It was only an informal party.
Don't be afraid to show yourself through speech and take every opportunity to speak to others in English and soon you will feel right at home in informal conversational situations.