A helicopter is a device that allows you to fly. Another word is helicopter. The special thing about a helicopter is that you can take off and land vertically with it.
You can also stop in the air with a helicopter. Aeroplanes, on the other hand, must always move forward, otherwise they crash. This is because air must always flow around the wings to create lift. In an aeroplane, the wings are rigid, so it needs speed to have lift. In a helicopter, the wings move. They turn, you say they rotate. that's why they're called the rotor.
Ideas for a helicopter have been around for a long time. It wasn't until the 20th century that engines became powerful enough for the helicopter. In 1922, Étienne Œhmichen from France built the first one that was reasonably stable in the air. Helicopters were then used in the Second World War, and in 1946 helicopters were also allowed outside the army.
Today, helicopters are not only needed in the army: most helicopters are used to observe things from the air and to rescue people. Besides, there are rich people who want to get to their destination much faster by helicopter than by car.