Matter

From AoPSWiki

Matter is defined as something that has mass and volume. There are unlimited states of matter, but only 5 have been achieved thus so far: Bose-Einstein Condensate (BEC), Solid, Liquid, Gas, and Plasma. Bose-Einstein Condensates have only been determined to exist recently, although the idea of them has been around since the time of, as the name suggests, Bose and Einstein.

Generally, as matter is heated, its particles gain energy to break the bonds between each other, and become more "independent", and the opposite goes for cooling.