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

What does the X4 mean in an PCIe Gen X4 NVME drive? m 2 pcie 4 0 in 3 0 slot My questions are: 1 Is the PCI-E NVME SSD compatible with my Z390 Godlike MOBO which has PCI-E slots? 2 m2 pcie 40 in 30 slot NVME SSD to PCIe Adapter Card 64Gbps M-Key X1 X4 Adapter for Desktop PC PCI-E GEN4 Full Speed If B 550m Pro4, the second slot is , not

m2 nvme slot  An 2280 solid-state drive , 22 mm wide and 80 mm long Connects to, Motherboard via one of: PCIe ×4; PCIe ×4; PCIe ×4; Serial ATA