What is defined as made by humans and not found in nature?

The term that best describes something that is made by humans and not found in nature is "artificial." This term implies that the item has been created through human ingenuity, often using materials or processes that do not occur spontaneously in the natural world. For example, artificial substances can include items like plastic or artificial sweeteners, which are manufactured in labs or factories rather than being derived from natural sources.

While "synthetic" also refers to human-made substances, it often specifically pertains to materials or compounds that are created to mimic natural substances or that consist of various materials assembled in a way that is not found in nature. Therefore, while "synthetic" can be closely related to "artificial," "artificial" encompasses a broader range of human-made items, including those that may not aim to imitate something natural.

The terms "natural" and "organic" refer to items that originate from nature, either in their native form or as products that adhere to certain natural processes or agricultural practices. This further reinforces that the correct answer is "artificial," as it distinctly identifies human creations rather than those derived from nature.