A curfew is an order which restricts people in their movements. It is very often an order which forbids people to be out on the streets after dark.
Curfews may be made by governments in times of war or civil unrest. This is supposed to stop violence.
Curfews may also be issued to young people. They are told that they have to be indoors after a certain time.
The word "curfew" comes from the French phrase "couvre-feu" which means "cover the fire". It was used to describe the time when all lamps and candles had to be blown out.