A Dry Cooling Tower is a heat rejection device that cools a working fluid (most often water or a water-glycol mixture) without direct contact with the air and without any water loss through evaporation.
Think of it as a giant, industrial-sized radiator, similar in principle to the radiator in your car. It uses the principles of sensible heat transfer (where heat is transferred, but the substance itself doesn’t change phase) as opposed to the latent heat transfer (evaporation) used in wet cooling towers.