Ventriloquism is the art of using your voice so that it seems to be coming from a dummy or puppet, rather than from your mouth. You should practice your ventriloquism before the school talent show: I can totally see your lips moving.
Someone who's an expert at ventriloquism is called a ventriloquist. This person has practiced until they've achieved the pinnacle of ventriloquism, the ability to "throw" their voice, so that it seems to be emanating from somewhere other than their own lips. Part of ventriloquism is learning to speak without moving your mouth. Another part is getting comfortable having a creepy-looking puppet sit on your lap and speak in your voice.