“Mountain bikes are built differently to withstand the tough terrain and to keep riders safe. The tires are typically thicker and more durable than a road bike’s in order to navigate unpaved environments, including roads and trails with rocks, logs, and branches. The handlebars are either flat or rise up, depending on preference, and the frame size should be matched to the size of the rider.
Source: New to Mountain Biking? Essential Tips to Gain More Confidence