A definite chemical composition refers to the consistent and well-defined proportions of elements or compounds present in a substance. It means that the substance has a specific and constant chemical formula, and its composition does not vary significantly. Compounds, in particular, have a definite chemical composition, where the elements that make up the compound are present in fixed ratios. This is in contrast to mixtures, where the composition can vary, and the proportions of components can change.

For example, consider the compound water (H2O). Water molecules always consist of two hydrogen atoms bonded to one oxygen atom, regardless of the source or the amount of water. This definite chemical composition is essential in determining the properties and behavior of substances. It allows us to consistently predict their characteristics, reactivity, and interactions with other substances, which is crucial in various scientific fields and industrial applications.