What is "reactive armour"

alt. (context British Canada English) Protective panels on a military armoured vehicle, which explode to disrupt the penetrating jet of a shaped-charge weapon. n. (context British Canada English) Protective panels on a military armoured vehicle, which explode to disrupt the penetrating jet of a shaped-charge weapon.

Reactive armour is a type of vehicle armour that reacts in some way to the impact of a weapon to reduce the damage done to the vehicle being protected. It is most effective in protecting against shaped charges and specially hardened kinetic energy penetrators. The most common type is explosive reactive armour (ERA), but variants include self-limiting explosive reactive armour (SLERA), non-energetic reactive armour (NERA), non-explosive reactive armour (NxRA), and electric reactive armour. Unlike ERA and SLERA, NERA and NxRA modules can withstand multiple hits, but a second hit in exactly the same location will still penetrate.

Essentially all anti-tank munitions (with the exception of HESH) work by piercing the armour and killing the crew inside, disabling vital mechanical systems, or both. Reactive armour can be defeated with multiple hits in the same place, as by tandem-charge weapons, which fire two or more shaped charges in rapid succession. Without tandem charges, hitting the same spot twice is much more difficult.