A ventriloquist's dummy is a facsimile of a human or animal etc that is operated by a man who throws his voice to make it appear that it is talking.
Puppet's can share similarities with the ventriloquist's dummy, but crucially not all puppets have to 'talk', they can be mute creations that give the illusion of being alive via a hand inserted in them or strings controlled from above by a man/woman to simulate movement.
Put simply, a ventriloquist's dummy HAS to have the illusion of speech. A puppet does not.
That's not just my opinion. It is FACT 100% true.