Metaphysical naturalism is a way of thinking about the world which says that all things come from nature. It doesn't involve believing in any kind of supernatural things like ghosts or gods. Instead, it focuses on understanding things in terms of the ways things work in nature. For example, physical laws like gravity. Metaphysical naturalism also involves thinking about things like meaning and morality as things that naturally happen in the world, rather than something that comes from an outside source.