Each aux out is connected to an effects unit and the signal is then returned into the desk. 2009, Rick Snoman, Dance Music Manual: Tools, Toys and Techniques, page 69:
(slang) The auxiliary audio connector of a sound system.
BE AWARE, reverbs should be in the end of your chain, as sends to auxes. Setting them first doesn’t mean they will be first in the chain. You just set up the auxes, then get back to the vocal channel to add EQs, compressors, etc. 2025 October 15, @natemixing, Twitter:
Hey, pass the aux. I'll play some music from my phone.