A more thorough explanation:

Definition: In accord with the regular course of things in the universe and without accidental or purposeful interference. Normal; proceeding from the regular character of a person or thing. Brought about by nature as opposed to artificial means. Inherent; not acquired or assumed. Indigenous; native. Of or relating to birth. Untouched by civilization; wild.

Examples:

• A natural death as opposed to murder.
• It is natural for a duck to fly south in the winter.
• A natural lake.
• Natural talent.
• The original or natural inhabitants of a country.
• Natural child as distinguished from adopted child.
• Only a small part of the forest remains in its natural state.

The examples illustrate that something is natural when it occurs without any interference or influence from humans. For example, a natural death is one that happens without any foul play or intervention. A natural talent is something that a person is born with and not something that they have learned or acquired through practice. A natural lake is one that has formed through natural processes, such as erosion and precipitation, rather than being created by humans. The natural inhabitants of a country are those that have lived there for generations and are not immigrants or settlers. A natural child is one that is born to their parents, rather than being adopted. A forest in its natural state is one that has not been touched or altered by humans.