Whats the difference between a normal BIKE and a MOUNTAIN BIKE?

A "bike" is a generic term meaning all bicycles, but they come in three varieties. First, the street bike, which has a slim, aluminum frame, and light, narrow, tubeless tires. next, the mountain bike, which has a thick, rugged aluminum frame, and heavy, wide tires for rough terrain, with the more expensive models also having a shock system. third, the cross-trainer. a light, slimmer bike, it is not as thin as the street bike, but not as wide as the mountain bike. it is used for both street use and some rugged terrain.