Condensation is the name of the process through which gas turns into a liquid. Three common states of matter exist: solids, liquids and gases. Matter, however, can change its state with the addition or subtraction of energy. The energy is usually in the form of heat.
Condensation occurs when a gas is cooled, at which time the gas turns into droplets of liquid. Condensation contributes to many common natural phenomena. It forms clouds which often give rain to the earth. Condensation also produces fog. The drops of water on a window's interior surface on a winter day also come from condensation. The change in matter occurs when the arrangement of the molecules changes. In a gas, the molecules are less organized than they are in a liquid.