The answer to 'what is central air' is central air conditioning, also known as a central HVAC (Heating, Ventilation, and Air Conditioning) system. This type of air conditioning system is designed to cool and dehumidify an entire home or building by using a network of ducts and vents to distribute conditioned air throughout the space.
Central air systems typically consist of an outdoor compressor/condenser unit that houses the refrigerant and a fan to circulate air, and an indoor air handler or evaporator unit that houses the cooling coil. The system uses refrigerant to absorb heat from the indoor air, which is then expelled outside, while the cooled air is distributed through the ductwork to the various rooms in the home. This allows for consistent, efficient cooling throughout the entire living space.