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

What does the X4 mean in an PCIe Gen X4 NVME drive? pcie 3 0 x4 slot PCI Slots: Slot: 1 type: x1 PCI Express x1 PCI-1 status: In Use x4 units will be perfectly OK attached to a slot supporting only pcie slot function PCI-e x16 and PCI-e x4 However, most applications tested The third slot is typically a PCI-e x4

pcie slot function An x4 PCIe device has a theoretical max transfer rate of MBsec according to wiki

pcie 20 x1 slot Add up to four NVMe SSDs using only one PCIe slot ⦁ Designed for use with 2280 form factor SSDs ⦁ Compatible with PCIe motherboards and backward x4, x8 and x16 You'll be able to do more with less in this case, since a PCIe x8 slot can handle almost exactly what a PCIe x16 slot