What is a latch relay, and where is it used ?

Latch relays are usually 2-coils, 2-position relays. The coil activation of one coil will transfer the armature and contacts to the other position. Conversely, activation of the other coil will transfer the armature and contacts back to its original position. The purpose of a latching relay is to conserve energy by pulsing the coil with a short pulse and removing the power once the relay has transferred. The latch relay lends itself easily to space applications because of minimal power drain on batteries.