What is the meaning of Rollercoaster?

An amusement ride consisting of a train on a track that rises, falls, twists and turns.

Any situation in which there are ups and downs, or violent changes.

rollercoaster, coaster (amusement ride consisting of a train on a track that rises, falls, twists, and turns)

rollercoaster, coaster (buggy on a track that rises, falls, twists, and turns)

Source: wiktionary.org