Which term refers to substances created by humans that are not found in nature?

The term that refers to substances created by humans that are not found in nature is "artificial." Artificial substances are intentionally designed or manufactured through human intervention, often to achieve a specific function or property that would not exist in natural materials.

In the context of nanotechnology, for example, artificial substances can include engineered nanoparticles developed for applications such as drug delivery, electronics, or materials science. These substances are typically tailored for enhanced performance or unique characteristics, setting them apart from natural substances, which occur without human influence.

Other terms provided, such as "natural," refer to substances found in nature and not altered or synthesized by human processes. "Organic" denotes compounds primarily consisting of carbon, typically associated with living systems, and does not inherently imply that they are man-made. "Synthetic" is often used interchangeably with "artificial" but typically emphasizes the chemical construction aspect of the substance, while "artificial" is more comprehensive, encompassing both chemical synthesis and broader manufacturing processes. Nonetheless, when asked specifically for human-created substances, "artificial" is the most encompassing and relevant term.