A tonne is a unit of measurement used to express mass or weight. It is equal to 1000 kilograms, which can also be expressed as one metric ton in the International System of Units (SI). The term comes from the French word “tonel,” meaning "ton," and was originally defined as the amount of weight a horse could pull. Today, it is commonly used in various fields such as shipping, construction, and manufacturing to express quantities of materials or goods.