AUI Full Form is Attachment Unit Interface. AUI is a physical connector interface between Computer Network Interface Card and an Ethernet Cable. It is the part of Ethernet standard located between MAC (Media Access Control) and MAU (Media Access Attachment Unit). It actually details how a cable would be connected to an Ethernet card. A coaxial cable is specifying by AUI to make junction with transceiver. AUI has a 15 pin connection that act as a signal path between a node and transceiver.
The AUI cable is approx. 50 meters long. In practice long cables are avoided for connection as MAU and MAC are in straight connection with each other. AUI connectors are rarely used due to the incorporation of MAU in computers itself. An AUI connector has a clip instead of thumbscrews that holds two connectors together. Apple Macintosh computers introduced a modified form of AUI called AAUI in 1991 but it discontinued in 1998. MAU is a transceiver that converts signal from Ethernet cable to and from AUI (Attachment Unit Interface).
In the modern world neither MAU nor AUI exists in interfaces as the cables are connected directly into an Ethernal socket through a host or router. The drop cable is connected via AUI port connector in NIC (Network. The other end of the cable mostly connects to the transceiver. The transceiver is then joined to cabling using a tap which then pierces the cable jacket and insulation in order to make a connection.