In HVAC, the term Ton is a term of Power (convertible to Kilowatts) as opposed to a unit of mass or weight (in conventional conversation). A ton is equal to the amount of energy it takes to melt 1 ton (2000 lb) of ice at 32 degrees over the course of 24 hours. 1 ton = 12 mbh
Example:
A rooftop unit that has a maximum capacity of 5 tons