Torsen is a company, best known for their gear-driven limited-slip differential design. While conventional differentials use clutch packs to allow the wheels to turn at different speeds, those clutches can wear out, and clutch-driven differentials can be unpredictable because the transition from static friction to kinetic friction happens quickly, and under different conditions depending on vehicle speed, differential temperature, weight distribution, etc.
A Torsen differential is entirely gear driven. It's quite an elegant design, and very sturdy. Because it's always in operation, there's no weird transition phase. It's also possible to dial in different bias settings by using different gears (bias being the maximum difference between inside and outside wheel speeds)