lsd???? tranny?

Hey im fixing to buy a jdm tranny to fit a b16a engine and the place im buying it from say's it'll give me a lsd tranny for 300 extra. Ok here's my question what is a lsd tranny? and what purpose does it serve?

that means the tranny is equipped with a limited slip differential.. something about better power transfer.. not too sure tho... but i know it's called limited slip differential :p

a limited slip differential puts the power to the wheel with the most traction unlike the open differentials that when you turn it just keeps spinning the wheel that loses traction first. it's better and if you have the money you should get it.