A roller coaster is a ride at a fair or amusement park. A roller coaster carries you quickly along a railroad-type track, sending you up and down steep hills and around sharp turns.
When you ride a roller coaster, you sit in an open-topped car, usually in a long chain of connected carriages that creep up and then plunge down hills. Some roller coasters take their riders upside down in loops or through scary tunnels. The earliest wooden roller coasters were built in the 1800s, and the first modern, steel roller coaster was constructed at Disneyland in 1959. In Japan, they're called "jet coasters."