The LS on Chevy Motors or LS Engines stands for "Luxury Sport".
LS engines are mostly in Chevy Sports cars but some trucks and other vehicles have the LS engine in them as well.
Some people have also swapped out the original Chevy 350 engine for an LS engine because the LS engine is supposed to be a much better engine.
Although if you do swap out an original Chevy 350 engine for an LS engine you need to replace and upgrade the computer so that the Chevy LS engine runs and runs properly.
I replaced a Chevy 350 engine in a 1970's Chevy Truck for an LS engine and it seems to run better and have more power and get better fuel mileage.
Also before the truck had a carburetor and now it has fuel injection which helps with the fuel mileage as well but it took some work and money to switch things over.