attachment unit interface
 
The AUI (attachment unit interface) is the 15-pin physical connector interface between a computer's network interface card (NIC) and an Ethernet cable such as 10Base-5 ("thicknet") coaxial cable. On 10Base-T Ethernet, a short cable is used to connect the AUI on the computer with a transceiver on the main cable. (In 10Base-2 or "thinnet" Ethernet networks, the NIC connects directly to the Ethernet coaxial cable at the back of the computer.)

Institute of Electrical and Electronics Engineers 802.3, the Ethernet standard, defines the AUI 15-pin physical layer interface. This interface is also called a DB-15 interface or a DIX interface (DIX refers to the three major companies who helped standardize Ethernet: Digital Equipment Corporation, Intel, and Xerox).