What do we call a substance that is composed of two or more metals?

The term used to describe a substance composed of two or more metals is an "alloy." Alloys are created by combining different metals to enhance their desired properties, such as strength, durability, or resistance to corrosion. Common examples of alloys include bronze, which is made from copper and tin, and steel, which is primarily iron with carbon added.

Understanding that "alloy" is the specific term denoting this combination helps clarify its definition and significance in materials science and engineering. An alloy is not just a simple mixture; it undergoes processes that can affect its microstructure, leading to enhanced characteristics compared to its constituent metals. The other terms provided do not accurately capture this definition or the technical nature of the materials involved.