Well there is a different and better definition but let me put it in simpler terms -
Basically a Product Designer is responsible for a product from its inception to market-ready stage. Let’s just say we want to produce Sunglasses, we will employ a Product Designer who will do all the research and work with the Design Team (Notice here) to make sure the product is coming according to their vision. Once the product is ready with all the testing and everything then the Product Designer must make strategies to get it properly marketed and make it ready for the prime time.
Basically you own a product and that product is like your child and anything happens, you have to take care of it.
This goes for Physical things like Sunglasses as I mentioned and also Digital Products like a new Website to manage your Taxes or sell these Sunglasses.
😎