what is a locking deferential?

Answer 1

It's called limited slip, posi-traction, locking differential, all basically the same. An option that forces both drive wheels to turn the same amount in the same direction. It is to keep from getting stuck in mud, snow and ice. Even if you jacked up one side of the car and put it in gear, the car would still go when you put it in gear.

Answer 2

A differential is an arrangement of gears that lets you send power to two wheels from one shaft without having to turn both wheels at the same speed. An open differential - the standard sort - has a limitation that's something of a nuisance: It cannot send more torque to one wheel than the other. So if one wheel has no traction, it can't send that wheel very much torque, and that keeps it from sending much torque to the other wheel. So you can get stuck in snow or mud with that.

There's a half-dozen different systems invented to get around this limitation. Some, such as the traditional limited slip differential, use a sort of brake in the gears to limit how much faster one wheel turns than the other.

A locking differential takes a somewhat different approach. There's a couple different kinds, but they usually act as an open differential (or a few, such as the Detroit Locker, send power to one wheel and let the other one freewheel) until something activates a mechanism inside that completely locks both shafts driving the wheels together so they must turn at the exact same speed. Some of them are activated by how much power you send to them, while others use electricity or compressed air.