A ton is a unit of weight or mass. . There are three primary varieties of ton : In the United States and Canada , however , a ton is defined to be 2000 l. To avoid confusion , the former is more specifically referred to as a `` long ton '' and the latter , a `` short ton '' ; neither should be confused with the metric ton ( tonne ) , which is 1000 k. While they do vary , a ton is generally one of the heaviest units of weight or mass referred to in colloquial speech .