In scientific terms, a substance is a specific type of matter that has uniform properties throughout and cannot be separated into other kinds of matter by physical means, such as filtration, distillation, or evaporation. Substances can exist in various forms, including solids, liquids, and gases. Each substance has distinct chemical and physical properties, such as melting point, boiling point, density, and chemical reactivity, that differentiate it from other substances. Examples of substances include water (H2O), salt (NaCl), oxygen (O2), and iron (Fe).