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

Getting to know PCIe and PCIe nvme pcie 4 0 in 3 0 slot PCIe devices are forward and backward compatible, therefore a PCIe SSD will still work on a PCIe motherboard and conversely a PCIe nvme pcie slot PCIe Gen for Professionals As mentioned earlier, PCIe is twice as fast as PCIe The same work which can be done by x16 slots of

nvme slot PCIe PCIe x 16 Slots 7 · 6 · 5 · 4 · 3 · 2 · 1 SSD Slots 5 x Ultra-Fast Storage：4*PCIe x4 slots; Efficient Overall Thermal：VRM Thermal