1. apparatus that extracts heat from a liquid that is at a higher temperature than its surroundings; can be used to transfer heat from a reservoir outside in order to heat a building;
WordNet (r) 3.0 (2006):
heat pump
n 1: apparatus that extracts heat from a liquid that is at a
higher temperature than its surroundings; can be used to
transfer heat from a reservoir outside in order to heat a
building