Acronym for Attachment Unit Interface connector, a standard 15-pin connector device for thicknet or 10Base5 cabling. The AUI connector on the free end of the drop cable attaches to the DB15 connector on the network interface card (NIC). The NIC has an AUI port connector for connecting the drop cable.
The other end of the drop cable typically connects to a transceiver. The transceiver is then joined to the thicknet cabling using a vampire tap that pierces the cable jacket and insulation to make a connection.