Yes, Sch is just an abbreviation for Schedule. That refers to the wall thickness of the pipe. Sch 40 is the standard thickness of PVC, and is usually white. Irrigation is often installed with a much thinner walled pipe, that is usually white as well, but the fittings used with irrigation are still Sch 40. Sch 80 is much thicker walled, and is usually gray in color.
The thread on the fittings makes the fitting much weaker, and it is very common for breaks to occur there, so having the thicker walled fitting adds strength.