Matter is any substance that has mass and occupies physical space (volume). It is composed of elementary particles such as quarks and leptons, which combine to form atoms-the basic building blocks of matter. Atoms then combine into molecules, elements, and compounds, which make up all the physical objects we encounter daily

. Matter exists in various states or phases, including solids, liquids, gases, and plasma. These states can change with temperature and pressure without altering the chemical composition of the substance. For example, water can exist as ice (solid), liquid water, or steam (gas)

. In physics, matter is distinguished from energy and massless particles like photons because matter has rest mass and occupies space. The Pauli exclusion principle explains why matter takes up space, as particles such as fermions cannot occupy the same quantum state simultaneously, giving matter its volume

. In summary, matter is the physical "stuff" that makes up the universe, characterized by having mass and volume, and composed of atoms and subatomic particles interacting through fundamental forces