The answer to 'what is air conditioner' is an appliance that cools and dehumidifies the air in a home or building. Air conditioners work by circulating refrigerant through a series of coils to absorb heat from the indoor air and expel it outside, while also removing moisture to keep the air cool and comfortable.
Air conditioners come in many different types, sizes, and configurations to suit the needs of different homes and buildings. They can be central units that cool the entire home, or window/wall units that cool individual rooms. They use electricity to power a compressor, fan, and other components that circulate the refrigerant and move the air.