If you don't know what it is you probably don't need/want it. It's almost obsolete. Go to the database and look up your area and see if anyone is using it.
ProVoice is a digital encoding scheme.
Note: it is a technology that is rapidly becoming obsolete.
If you don't have anyone using it in your area, forget about it....
ProVoice is digital modulation used on some EDACS trunked systems. If you don't monitor any EDACS systems with digital voice, then you don't need ProVoice.