Massif

A massif is a part of the Earth's crust that has been pushed up. Usually this happens when continental plates press against each other. One set of rocks goes up, the other goes down towards the Earth's mantle. 
The word "massif" means a block of mountains formed by this process, and surrounded by fault lines. Linear mountains like those on the western side of the Americas are usually not called massifs. They are called mountain chains.
An example of a massif is Saser Kangri in the Karakoram which is made up of six mountains. The most famous example of a massif is the Himalayan group.