means A unit of weight equal to roughly 1,000 kilograms (metric) or 2,000–2,240 pounds, depending on which system you're standing in; also used loosely to mean 'a huge amount.'

from From the same source as 'tun,' an Old English word for a large cask or barrel — the kind used to ship wine. The word measured not weight but capacity: a 'tun' of wine was a barrel of a standard, very heavy size. Over time the spelling split — 'tun' kept the barrel, 'ton' took the weight — but both trace back to a Germanic root, possibly borrowed in turn from Latin 'tunna' (a cask). So the heaviest little syllable in English began life as something you could pour.