What is the term for the matter that an object is made of?

The term that most accurately describes the matter that an object is made of is "material." In a general sense, material refers to any substance or mixture of substances that constitutes an object. This encompasses a wide range of items, including solids, liquids, or gases, and includes the various elements and compounds that can be found within.

While "substance" is also a relevant term, it usually refers to a specific form of matter with a uniform and definite composition. In contrast, "material" can refer to both pure substances (like elements and compounds) and mixtures, making it a broader category.

"Element" specifically pertains to the basic building blocks of matter that cannot be broken down into simpler substances, while "compound" refers to substances formed when two or more elements are chemically bonded. Therefore, in the context of describing what an object is made of in a more inclusive manner, "material" is the most appropriate choice.