The definition of a 20 ton AC is a unit of measurement used to measure the cooling capacity of an air conditioner. It is equal to 20,000 BTUs per hour, which is the amount of energy needed to cool a space of 1,000 square feet. A 20 ton AC is typically used in commercial buildings and industrial settings, as it is able to cool large areas quickly and efficiently. In residential settings, a smaller unit, such as a 5 ton AC, is more commonly used. It is important to note that the size of the unit does not necessarily indicate its cooling capacity, as other factors such as the type of refrigerant used and the efficiency of the unit also play a role. When selecting an AC unit, it is important to consider the size of the space to be cooled and the desired temperature.