XAUI is a standard for extending the XGMII (10 Gigabit Media Independent Interface) between the MAC and PHY layer of 10 Gigabit Ethernet (10GbE). XAUI is pronounced "zowie", a concatenation of the Roman numeral X, meaning ten, and the initials of "Attachment Unit Interface".
The XGMII Extender, which is composed of an XGXS at the MAC end, an XGXS at the PHY end and a XAUI between them, is to extend the operational distance of the XGMII and to reduce the number of interface signals. Applications include extending the physical separation possible between MAC and PHY components in a 10 Gigabit Ethernet system distributed across a circuit board.