The story
History: facts, each with its source
Wikipedia says the name blends the words torque and sensing, and that the American Vernon Gleasman invented it, from a design he patented in 1958. The Gleason Corporation made it, and the trademarks are now held by JTEKT Torsen North America.1
Wikipedia says a Torsen can share torque between the front and rear axles of an all-wheel-drive car, or between the left and right wheels of one axle. Its torque bias ratio caps how uneven the split can be: at 3:1, one side can get up to three quarters of the torque and the other one quarter.1