What is a stone?

ive heard ethnic group say that they want to gain a stone. or they're a 9 stone. i assume its some brand of weight----like lbs. or something. where do ppl influence that??? a stone. the only stone that i kno is a rock.What is a stone?
A stone is a calculate of weight most commonly used surrounded by Great Britain (and certain colonies). A stone is 14 lbs.
14 pounds or 6.38 kg
It's the british route of measuring your bulk, like you own kilos, we have stone and pounds.