Noun > Roller coaster
(count)
1 : a ride at an amusement park which is like a small, open train with tracks that are high off the ground and that have sharp curves and steep hills
We went for a ride on the roller coaster.
a roller-coaster ride
2 : a situation or experience that involves sudden and extreme changes
The divorce was an emotional roller coaster for both of them.
He’s had a roller-coaster career. (=a career with many ups and downs)