What does the X4 mean in an PCIe Gen X4 NVME drive?

After a quick Google search, I found this article which explains that: a PCIe x16 slot can theoretically hit approximately 32 gigabytes

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pcie x1 in x16 slot In theory, PCIe doubles the data transfer rate from 8 GTs to 16 GTs in comparison to , which then corresponds to about 2 GBytes per

pcie gen 4 in gen 3 slot A PCIe graphics card will work in a PCIe motherboard slot at PCIe speeds For PCIe graphics cards, maximum graphics throughput