What does it mean to be "natural"?
It depends how and in what situation you are using it. In general, natural means "of nature". When we use it in Standard English, it usually refers to anything that is not using artificial ingredients or processes. "Natural foods" for example have only pure ingredients, without preservatives, colorings or other additives.
"Natural world", on the other hand refers to those things that occur in nature - animal kingdoms, the outdoors, food chains, ecosystems, and most plants and animals would all be considered part of the natural world.
Lastly, we sometimes use natural in the sense that something happens, comes to us or is achieved automatically, without effort, such as a baseball pitcher being a "natural" - already talented, in other words, or a natural singer who was born with a very strong voice.