A substance is essentially a species of matter having a definite chemical composition . A number of substances can combine to form a mixture. Pure substances are composed of a single element or compounds. Combinations of different substances are called mixtures. Homogeneous mixtures are mixtures of two or more compounds (or elements) that are not visually distinguishable from each other.
In the classical physics observed in everyday life, matter is any substance that has mass and takes up space by having volume. This includes atoms and anything made up of these, but not other energy phenomena or waves such as light or sound. More generally, however, in (modern) physics, matter is not a fundamental concept because a universal definition of it is elusive; for example, the elementary constituents of atoms may be point particles, each having no volume individually.
