Aux
Aux or AUX may refer to:

Science and technology
Auxiliary connector or AUX jack, typically used for analog audio signals
Aux/IAA repressors, related to auxin plant hormones

Computing
AUX: (for auxiliary), a DOS text device
AUX (CONFIG.SYS directive), changes assignment for AUX: device in DR-DOS
A/UX, a Unix operating system by Apple

Other uses
Auxiliary (disambiguation) (abbreviation)
Aux (TV channel), a Canadian music TV channel
Araguaína Airport (IATA airport code), Tocantins, Brazil