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

Run PCIe x8 NIC in x4 slot? - Hardware Hub x4 slot x4 NVMe Support Rated Maximum Sequential Read 3500 MBps Rated Maximum Sequential Write 3000 MBps Terabytes Written Rating 440 TBW Warranty Length 5 x4d slot slot with x4 PCIe Gen3 Key M slot with x2 PCIe Gen3 Key E slot, 1 x4 + 3 x1 USB*, USB Type-C connector: 2x USB

honey gems slot X4 14 15 16 17 18 19 20 21 22 23 24 FortiGate 200F POWER HA ALARM STATUS 3 2 slots, NP6XLite and CP9 hardware accelerated FortiGate 201F