A cryovolcano is a spot that erupts a substance that is liquid or gaseous at cold temperatures (cold relative to us). Example substances are water, methane, or ammonia. The eruption, for example, could be a water plume escaping through a gap in an outer ice layer. The presence of such eruptions can be called cryovolcanism.
They are evident on some planets and moons that are at much lower temperature than Earth and that have deposits of such materials covered by a solid layer. Moons on which cryovolcanism has been observed include Triton, Enceladus, Europa and Ganymede.