09 Mixers: Aux Sends Aux sends - auxes for short - allow you to take a piece of the signal from each channel and create mixes which are separate from the one at the mixer's main output.
For example, you can use auxes, to make a mix for a vocalist to listen to in their headphones while they're recording.
You give them the exact balance of instruments that they are comfortable with, without having to mess up the main mix.
Alternatively, you can use auxes to add effects.
If you want to add the same reverb effect to every element of a drum kit, you can use an aux send to draw off some of the signal from each element of the kit.
Then you send that little mix to the reverb unit.
Smaller desks may have only one or two aux sends while larger analogue and digital ones may have 8 or more.