Armour (or armor U.S.) is a protective covering or clothing to prevent injury from attack. Armour can be worn by a person, or it can be used to protect machines, animals, even buildings. Armour has always been made from the strongest materials available at the time, but weight has always been a problem. Early body armour was made from leather. Later, metals were used (e.g. mail or plate armour). Some modern armour, like bullet-proof vests, are made from plastics that do not stretch or break, such as Kevlar. These plastics may be woven into a cloth and used in layers, which makes them even stronger.
Armour put on vehicles is usually made of metal and can include one layer over another with open spaces in between (spaced armour) or multiple layers of metal; ceramics (baked clay), and other materials. Another type of armour uses blocks of explosive that explode when another explosion goes off near it. This explosive armour protects by pushing against the other explosion. Vehicle armor is often angled to increase the amount of armour that must be shot through to get inside and to make the shot bounce off rather than piercing the armour.
Tanks have the heaviest armour of all land vehicles. Other military vehicles have armour, but not as much as a tank.