Aux send
A tap on a mixer channel that sends a copy of the signal to a shared bus, usually feeding an effect many channels have in common.
Insert effects sit directly in the channel's signal path and process everything passing through. A send leaves the original alone and passes an adjustable amount onward — classically to a reverb bus. Ten channels can then share one room, which sounds more cohesive and costs a fraction of the CPU of ten reverb instances.
Sends can be taken before or after the channel fader. Post-fader follows the channel down when it's pulled back, so the echo doesn't linger on its own. Pre-fader doesn't, and is used for monitor mixes: the musician in the headphones rarely wants their mix changing every time the engineer touches a fader.