Form of armor used as an add on to existing metal plate on tanks and armored personnel carriers. Ablative armor is specifically designed to be destroyed by incoming missile or light cannon fire, thus protecting the vehicle's primary armor from further damage. Most Russian MBT's (main battle tanks,) such as the T-80 and T-72 use ablative armor extensively in the form of large olive drab rectangles seemingly strapped at random onto the front, rear and turret areas of the machine. Use of ablative armor is particularly effective against smaller shaped charge warheads as fielded by infantry crews with anti-tank weaponry.
The underlying physics of ablative armor involve nothing complicated more than the absorption of kinetic energy generated by a warhead detonation.
As the missile detonates it creates a shock wave in front of it designed to compromise the skin of the vehicle at a specific point. This then allows the missile to continue penetration of the target, at which point the warhead will complete the detonation cycle inside of the target. Ablative armor is essentially a throwaway solution to such shape charge warheads. Unfortunately it is not effective a solution as it would seem, given that the easiest way to overcome such protection is simply to build anti-tank missiles with larger warheads.
Ablative armor differs directly from reactive armor, (which actually explodes, thereby creating another shockwave to counter the effects of the incoming missile,) in that they are completely passive systems. It has a direct advantage in that it is extremely cheap and simple to implement, tank crews simply bolt or strap the additional armor onto the tank and drive away. If and when damaged they remove the effected sections and replace it with new material. Significant weight will be added to the vehicle however this is not seen as a disadvantage by most tank crews in hostile situations where ablative armor is used.
The closest equivalent to ablative armor for a human being would be the leather jackets and coveralls worn by motorcycle riders which are designed to be destroyed aesthetically by a road accident but still prevent damage to the underlying skin.