Aux (Auxiliary Channel)
Definition
A secondary signal path used to route audio to a shared destination — typically a headphone mix for performers, a send to an effects processor, or a submix. "Aux" and "send" are often used interchangeably in modern DAWs.
In Simple Terms
A secondary output used for headphone mixes during recording or for sending audio to shared effects like reverb. In modern DAWs, aux and send mean the same thing.
In Practice
A headphone aux mix is built separately from the main mix so the drummer can hear more of their own instrument without changing the engineer's balance at the main output.