Gases are one of the four fundamental states of matter, alongside solids, liquids, and plasmas. They are characterized by their ability to expand and fill any container, taking the shape and volume of that container. The molecules in a gas are in constant motion and are much farther apart compared to those in solids and liquids, which allows gases to be compressible and to flow easily. The behavior of gases is described by various laws, such as Boyle's Law and Charles's Law, which relate pressure, volume, and temperature. Gases play a crucial role in many natural processes, including respiration in living organisms and the formation of weather patterns in the atmosphere.