Naturalism commonly refers to the philosophical

Philosophy

Philosophy is the study of general and fundamental problems, such as those connected with existence, knowledge, values, reason, mind, and language. Philosophy is distinguished from other ways of addressing such problems by its critical, generally systematic approach and its reliance on rational...

 viewpoint that the natural universe and its natural laws and forces (as opposed to supernatural

Supernatural

The supernatural or is that which is not subject to the laws of nature, or more figuratively, that which is said to exist above and beyond nature...

 ones) operate in the universe, and that nothing exists beyond the natural universe or, if it does, it does not affect the natural universe that we know. Followers of naturalism (naturalists) assert that natural laws are the rules that govern the structure and behavior of the natural universe, that the universe

Universe

The Universe is commonly defined as the totality of everything that exists, including all matter and energy, the planets, stars, galaxies, and the contents of intergalactic space. Definitions and usage vary and similar terms include the cosmos, the world and nature...

 is a product of these laws and that the goal of science is to discover and publish them systematically.

Note that the term "naturalist" is also used to describe a person involved with the scientific study of (or education about) nature and the natural world (particularly fields of botany and zoology), as distinct from someone holding any specific philosophical position.