In terms of cars, locking and limited slip are used relatively interchangeably. However, Limited Slip is activated via input from the drive shaft and the Locking Differential is via loss of traction on one side or the other. Also, Limited Slip has clutches in it for additional traction, while locking doesn't. This means what a limited slip will only engage all the wheels if it sense a loss of traction (in a sense) to send power to the other wheels, while locking is engaged all the time. Basically, if you have very uneven terrain, you want a locking differential.