The term for a pure substance that cannot be broken down into simpler substances is an element. Elements are the fundamental building blocks of matter, represented in the Periodic Table. Each element consists of atoms with the same number of protons, which defines their chemical properties. For example, carbon, oxygen, and gold are all elements, each with unique characteristics. Understanding elements is essential for studying chemistry, as they combine to form compounds, impacting various fields ranging from materials science to biochemistry.