A stannary is a region containing tin works within Devon and Cornwall.
Devonshire stannaries are generally referred to by the names of local towns, in this case Tavistock.
Tavistock was a stannary town in history as it refined, assessed, coined and sold tin. The proceeds of this was either passed to the Duchy of Cornwall or the Crown. King Edward I's 1305 Stannary Charter established Tavistock, Ashburton and Chagford as Devon's stannary towns, with a monopoly on all tin mining in Devon.