Mountain bikes are the most versatile bicycle type. Mountain bikes are primarily designed for off road use, the bicycles can also be used for commuting or recreational cycling. Mountain bikes often feature suspension on the front - called hard tail mountain bikes, and also on the rear - called dual suspension mountain bikes.
The amount of suspension travel dictates the type of riding, as a guide there is 120mm for cross country, 140mm for trail riding, 150mm for all mountain, 170mm for free ride and 180mm+ for downhill.
The more travel a bike has, does not mean better, as the more travel a bike has means a bike weighs more too - Choose a bike that suits your requirements.