NEED TO KNOW___UNITY GAIN ???

WHAT IS UNITY GAIN ???

I have 63 pedals on my board. When I go from one to another it would be insane if they were all different volume levels. A classic Boss CE2 Chorus does not have   a volume control. It is designed so it will be not be any louder or quieter when it is off or on. It short it is set to unity gain. I set ALL my pedals to never be louder than my bypass clean sound. On some tunes I do set a pedal a bit turned down when it is only played while I am singing. When I cease singing during the bridge, solo etc. I turn on a different pedal set to unity gain with my amp. Meaning my pedals are never louder than my amp weather they are off or on.