Substance refers to a material with distinct properties and characteristics. It can be classified into two main categories: elements, which are pure substances made of only one type of atom, and compounds, which consist of two or more different elements chemically bonded together. Substances can exist in different states, including solid, liquid, and gas, depending on temperature and pressure. In chemistry, the study of substances involves understanding their composition, structure, and behavior. This knowledge is essential for various applications, such as developing new materials, pharmaceuticals, and understanding biological processes. The properties of a substance, such as density, melting point, and solubility, help scientists identify and utilize them effectively.