In horology, a tourbillon (/tʊərˈbɪljən/; French: [tuʁbijɔ̃] "whirlwind") is an addition to the mechanics of a watch escapement to increase accuracy. It was developed around 1795 and patented by the French-Swiss watchmaker Abraham-Louis Breguet on June 26, 1801. In a tourbillon the escapement and balance wheel are mounted in a rotating cage, in order to negate the effects of gravity when the timepiece (thus the escapement) is stuck in a certain position. By continuously rotating the entire balance wheel/escapement assembly at a slow rate (typically about one revolution per minute), the tourbillon averages out positional errors.
Source Wikipedia : https://en.wikipedia.org/wiki/Tourbillon