Matter is anything that takes up space and has mass. It is made up of particles and can be found in four states: solid, liquid, gas, and plasma. Matter has shape, volume, and mass. Solids have particles that are tightly packed and do not change shape. Liquids have particles that are loosely packed and can flow and change shape but maintain a constant volume. Gases have particles that are far apart and spread out, changing both shape and volume. Matter can change states when heat or cold is added through processes like melting, freezing, boiling, and condensation.