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

What happens if you use a PCIe NVMe SSD in a PCIe m 2 4 0 in 3 0 slot Helpful Tip: Keep in mind that an SSD is only compatible with a motherboard that supports a slot PCIe 2280 NVMe form factor; 250GB m2_1 slot First of all, I know that a PCIe 4 SSD NVMe will be running at gen 3 speeds and bottlenecked by the PCIe 3 slot But I'm wondering if there are

m2 vs nvme slot The SSD should work because the _2 slot supports both NVME and SATA but the speed will of cause be lower than the main _1 port Another