Air conditioning (usually called AC, a / C or air conditioning) is the process of removing heat and water from the interior of the living space to improve the comfort of the occupants. Air conditioning can be used in home and business environments. This process is most commonly used to achieve a more comfortable internal environment, usually people or animals. However, air conditioning is also used to cool / dehumidify rooms equipped with thermal electronic devices (such as computer servers, power amplifiers), and even to display and store artwork.

Air conditioning usually uses fans to distribute conditioned air to occupied spaces such as buildings or cars, in order to improve thermal comfort and indoor air quality. Based on electronic refrigerants, the range of AC equipment is very wide, which can provide a small device for an adult to cool down, a small bedroom to cool down, and the roof of the office building of the whole building to install large-scale equipment. Cooling is usually achieved by a refrigeration cycle, but sometimes evaporation or natural cooling is used. Air conditioning systems can also be built based on desiccants (chemicals that remove moisture from the air) and underground pipes that distribute heated refrigerant to the ground for cooling.

In the most general sense, air conditioning can refer to any form of technology that can change the state of the air (heating, cooling, (dehumidification), cleaning, ventilation or air flow). However, in normal use, "air conditioning" refers to the system of cooling air. In a building, a complete heating, ventilation, and air conditioning system is called heating, ventilation, and air conditioning (HVAC - as opposed to AC)