Pre-fader, Post-fader
On a mixer with auxiliary send mixes, the send mixes are configured pre-fader or post-fader.
If a send mix is configured pre-fader, then changes to the main channel strip fader does not affect the send mix. In live sound reinforcement, this is useful for stage monitor mixes where changes in the Front of House channel levels would distract the musicians. In recording and post production, configuring a send to be pre-fader allows the amount of audio sent to the aux bus to remain unaffected by the individual track fader.
If a send mix is configured post-fader, then the level sent to the send mix follows changes to the main channel strip fader. This is useful for reverberation and other signal processor effects.
Read more about this topic: Fade (audio Engineering)