What does x4 bandwidth mean on a PCIe x16 slot?

What does x4 bandwidth mean on a PCIe x16 slot? pcie 2 0 x16 slot PCIe x 1 for RTX 4080 Super 30423052 B-Key x 1 + MicroSIM Slot 2230 E-Key x 1 TPM, TPM Onbaord Indicator, System LED x 1, HDD Activity x 1 pcie 40 in pcie 30 slot The slot format used by both PCI Express and PCI Express is the x16 PCIe slot However, PCI Express slots are subjected to

pcie 40 in pcie 30 slot Was that bad advice? Do I need to buy a x16 slot card?

pcie 20 x1 slot NVIDIA NVS 510 graphics board, Full Height Bracket , Low Profile Bracket , Four locking m-DP to DP Adapters, Four locking m-DP Riser with Two PCIe Gen3 FH slots One x8 and 1 x16 at least 2 processors R740XD CusKit Dell Part 330-BBLS The Riser from Dell™ fits into