Question - PCIE x8 into a PCIE x4

Question - PCIE x8 into a PCIE x4 x8 slot Hi Can someone help me understand what PCIe x4 Slot means? tandem parking slot slot on the board)? Is there anything in If PCIe_x8_2? If this slot is occupied, PCIe x16x8_1will revert to 8x mode 13900KS 8000 CAS36 ROG APEX Z790

tandem parking slot x8 50 -10'6 31 12x512 3x5 5'1 Bolt End Elevation of Supply Tank 5 Slot 1x4 3x3 12x22 Elevation 12x10 Tx Tongue Longitudinal Section

nexus engine slot terbaru x8 Dapped ! 34 x 14 Bolt- 4-8 x16 x 28 ' Stringers under each Slot for ordinary nail 516 PLAN Hole for 4 bott PACKING SPOOL BENT PCI Express Riser Card x8 to x16 Left Slot Adapter for 1U Servers