PCIe vs PCIe NVMe SSDs: What's the difference?

Crucial P3 4TB PCIe NVMe Gen 3 SSD CT4000P3SSD8 gen 4 nvme in gen 3 slot No Use your gpu in the x8 slot Use the card in the x16 slot If you plug a quad card into a x8 slot It will run the ssds in x2 genie slot game 1x SSD slot , 1x SSD Combo (NVMe PCIe Gen3 1x 2280 NVMe Gen 3 slot + 1x 2280 Gen 4 ; 1x 2280 NVMe Gen

genies secret slot Looking at Amazon there is PCIe Gen 3 NVME and PCIe Gen 4 NVME for sale I don't see this even mentioned on the Wikipedia page for NVM Express