What is the difference between PCIe Gen 3 and PCIe Gen 4?

Hi there, I'm trying my first build and I bought a samsung 980 PCIe NVMe SSD which is a PCIe Gen x4, NVMe interface

Gen4 x4), 1 ; 2 USB Gen2 , 8 USB Gen1 ; Dragon LAN *Not compatible with AMD Athlon

nvme 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

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