Matter is anything that occupies space and has mass, with properties including size, shape, color, length, and volume. Matter can be definite or indefinite in volume and shape, and comes from both living and non-living things, including being found underground, coming from trees, animal skins, and plants, and being transformed into materials like oil into plastic, wood into paper, and sand into glass. Mixtures occur when two or more kinds of matter are combined but can be separated, unlike changes where a material is transformed into something different in a non-reversible process.