Attachment Unit Interface

The Attachment Unit Interface (AUI) is a physical and logical interface defined in the IEEE 802.3 standard (additionally published in FIPS PUB 107) for 10BASE5 Ethernet and the earlier DIX standard. The physical interface consists of a 15-pin D-subminiature connector that links an Ethernet node's physical signaling to the Medium Attachment Unit (MAU), sometimes referred to as a transceiver.

Source: Wikipedia — Attachment Unit Interface (CC BY-SA 4.0)