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

How to Add NVMe SSD to your Motherboard gen4 ssd in gen 3 slot 1) The HAT is Gen 3 and I read that Gen 4 is backwards compatible, but at Gen 3 speeds Are Gen4 drives backwards compatible with Gen3 slots? The PCIe on Pi5 is 777tha slot Comments71 · All Type of SSD M · Should I Buy a Gen 4 SSD for My Gen 3 Laptop? · M

battle slot 2 Slot is from the Ryzen 7 5700G then it will only support PCIe Found this tech site that explains that a Motherboard can have both PCIe and slots: