Looking for a deeper explanation on the pin-slot alnment

pin slot4 pin fans can run in 3 pin fan slots and will only go in one way since the header is keyed but will only run via voltage control. Most fans don't mind but have slhtly less range ofSapphire PinSlot · Recessed commerical grade COB LED downlht in a compact desn · Hh quality aluminium heatsink and body for durability and longevity