A refrigerant is a heat transfer medium – a substance that can absorb heat from a source, transport it and release it elsewhere.
The name comes from an early application in refrigerators. Unwanted heat is absorbed from the storage compartment, pumped to external pipes and thus dissipated to air. The same principle is also used in air conditioners and heat pumps.
Other physical properties of refrigerants find applications beyond heat transfer. In particular some make good aerosol propellants, used in spray cans, fire extinguishers, insulation foam manufacture, and notably in “metered dose inhalers” to control asthma and other breathing problems.