Gravel biking is a type of cycling that takes place on unpaved or gravel roads. It's a bit of a hybrid between road biking and mountain biking, with bikes being lighter than mountain bikes, with no suspension and more speed than an MTB on the same terrain. And it offers a unique challenge and adventure for cyclists. Gravel biking allows riders to explore more rugged terrain and remote areas, away from the hustle and bustle of traffic. It requires a different set of skills than traditional road biking, such as technical bike handling, route finding, and a higher tolerance for rough and unpredictable surfaces. It's perfect for those who love the thrill of exploring the great outdoors on two wheels.
You can buy a dedicated gravel bike, an endurance bike (a cross between a road bike and a gravel bike), or just put larger tires on a road bike and ride gravel and other surfaces.
Gravel Bikes that are specifically made for gravel may have a slightly more relaxed frame geometry than a road bike with a lower center of gravity, longer wheelbases, more MTB-like gearsets and ranges, ability to take wider tires, and possibly a few other things not found on road bikes.
And don't get caught up in the 'gravel' part of 'gravel biking' - these are versatile, all-terrain machines that can be used on anything including, of course; any kind of gravel but also dirt, grass, sand, mud, snow, and a variety of paved surfaces. Like the examples below: