Are you referring to multiple instruments or other signals coming out of a single source? Your question is a little vague. The output of any signal is all relative to the number of inputs, whether it be a guitar, amp or mixer. These all have an input that is pretty easy to understand but their output is wherever you put it. Some of these might have multiple outputs because they go to multiple sources; I.E. a mixer during a live performance usually has 2 or more outs. The first of these is the house or what you hear as a member of the audience. The second is the monitor, this is what the musicians on stage hear. All other possible outputs depend on the size of the mixer and the number of outboard gear being used. Some venues don't have any outboard gear at all(usually the cheap ones!). I hope this didn't create more questions than it answered.