me and my friend were goin off roading and a dude there told my friend that he needed atleast one locker what is a locker?

 

a locking differential locks both wheel so they have to turn the same speed. most vehicles come factory with an open differential so one wheel can turn faster than the other which is why when you put 1 wheel in the mud and hammer the fun pedal it only spins that one wheel and the other is not moving. so when you lock your rear end it makes both rear wheels turn at the same speed. its nice to have in alot of 4 wheel drive places.