XAU

XAU may refer to:


 * The ISO 4217 standard code for one troy ounce of gold, considered as a currency.
 * A symbol for the Philadelphia Gold and Silver Index, an index of precious metal mining company stocks that are traded on the Philadelphia Stock Exchange
 * An authentication protocol library for X Window System
 * A Portuguese slang word, also written as Tchau or simply Chau, from the Italian word Ciao, meaning goodbye/bye.