An air-conditioning system can precisely control temperature, humidity and air quality although more commonly the phrase is used to describe a system that cools.
Generally air-conditioning comes in three standard variations:
Centralised air systems
Heating and cooling is performed in a central location and distributed via ductwork.
Partially centralised air/water systems
Centrally cooled or heated air is further heated or cooled on entry to rooms.
All operations are performed locally.
Within these three generic examples more specific air-conditioning systems can be specified, to provide precise function for specialist uses.