NIC (network interface card)
Beginner
The part that connects the server to the network cables.
Novice
A card that turns data in memory into network packets and back. AI servers often have one fast NIC per accelerator so each can talk to other servers.
Expert
A PCIe endpoint with Ethernet or InfiniBand ports, usually RDMA-capable. With GPUDirect-style peer-to-peer it can read and write accelerator memory directly, which is why NIC and accelerator often share a PCIe switch.