### Instruction:
What type of terrain is a gravel bike used for?

### Input:
A gravel bicycle is a type of bicycle intended for gravel cycling, including gravel racing. They are also sometimes known as "adventure bicycles", particularly ones intended for harsher off-road terrain.

While bicycles have been used for riding on such roads since bicycles were invented, the "modern" gravel bicycle, as a category, evolved in the 2000s, adopting technology from road bicycles, cyclocross bicycles and mountain bikes. They also share many characteristics of touring bicycles, such as relaxed geometry, wide tires and wide-range gearing.

### Response:
Gravel bikes are a do-it-all kind of bike. They are effective on a wide array of terrain, ranging from smooth roads to singletrack trails, but thrive on harsher off-road terrain.