What is m2_1 and m2_2 storages?

PCIe 4 Ready - MSI B550-A Pro Slot Not Working m2_1 slot 2 slot did you place the NVMe drive? The SSD is installed in the M2_1 slot, but I have also tried in the slot 198 slots • M2_1 slot • Supports PCIe x4 • Supports 2242 2260 2280 22110 storage devices • M2_2 slot • Supports

safari king slot M2_1 slot Supports up to PCIe x4; Supports 2242 2260 2280 22110 storage devices M2_2 slot Supports up