PCIe, short for Peripheral Component Interconnect Express, is a high-speed expansion card interface designed to replace the older PCI, PCI-X, and AGP standards. It offers higher data transfer rates compared to these legacy slots, making it the best choice for a high-speed NIC, which requires fast data transfer capabilities to operate effectively. PCI and AGP are older standards with lower bandwidth and are not suitable for high-speed NICs often used in modern office workstations for demanding network tasks.