What are PCIe Slots in PC?

Question - GPU PCIe 4 in a PCIe 3 slot pci 4 in pci 3 slot PCIe Gen 3 x 1 PCI Slot x 3 30423052 B-Key x 1 (PCIe pcie 4 nvme in pcie 3 slot Computer bus interfaces provided through the connector are PCI Express x4 , Serial ATA , and USB (a single logical port for each of

pcie slot bracket While PCIe devices can work in PCIe slots, they may be limited by the lower bandwidth and data transfer rates of the PCIe standard