What is a PCIe SSD?

Hi, I currently am using a Pi 5 and I have connected via a Blue USB slot an External SSD enclosure, with an PCIe Gen 4 NVMe SSD in it

Reviewing the AMPCOM NVME SSD to PCIe Adapter Card, 64Gbps SSD PCIe4

m2 sata slot The M2 Ultra chip connects to the PCIe slots through a PCIe switch and provides 24 lanes of gen 4 bandwidth Pool A provides a maximum of 16

m2 slot types Some motherboards will only have one slot that can run at NVMe PCIe bandwidth, whereas others may be restricted to using SATA bandwidth