These days, Shimano derailleurs are referred to as either top- or low-normal. It used to be “the way it always was” and Rapid Rise. And sometimes, high and low. But now, top and low.

Top-normal - The derailleur as it always has been, as cable tension is released spring tension forces the chain to a smaller cog (higher gear). Downshifts to a bigger cog (lower gear) are done via cable tension pulling on the derailleur parallelogram and pushing the chain up the cassette.

Low-normal - New school, where the spring tension is reversed. As cable tension is released spring tension pushes the chain to a larger cog (lower gear). The lowest gear is the “normal” orientation of the derailleur when there is no cable tension.