Ablative armour is a type of protective hull plating used on starships in Star Trek. Placed on the outer hull of a starship, it possesses the capability for rapidly dissipating the energy impacts from directed energy weapon fire and protecting the ship's interior. The Star Trek: Deep Space Nine Technical Manual defines ablative armor as armor designed to disintegrate at a controlled rate under directed energy blasts, providing an additional layer of defense for starships. This armor was first seen in use protecting an unshielded Defiant against Klingon disruptor fire in the Star Trek: Deep Space Nine episode "The Way of the Warrior".
In real science, ablative materials are defined as "any material that possesses a capability for rapidly dissipating heat from a substrate". Ablative shielding is indeed used today in 21st century spacecraft and probes. The heat shields in the Space Shuttle, for example, are constructed of ablative material. The Whipple Shield - the first spacecraft shield ever implemented - consists of of an aluminium bumper placed in front of the spacecraft, thus allowing it to absorb the initial impact. The bumper shocks the projectile and creates a debris cloud containing smaller, less lethal, bumper and projectile fragments. Additional layers, containing ablative material such as Nextel and Kevlar, further shock and pulverize the debris cloud such that any fragments reaching the rearwall are benign.
Whipple shield used on NASA's Stardust probe