Solid

• A solid is the most compact and dense state of matter. Solids do not flow and usually don't change shape easily. The atoms or molecules in a solid are sometimes arranged in a regular pattern. The movement of individual particles in solid matter is limited. Very cold solids may be almost motionless on the atomic level. Adding heat to a solid is one way to cause it to transition into a liquid.
  
  

Liquid

• Matter in a liquid form is still dense, but lacks the neat and regular arrangement of a solid. The most distinctive quality of a liquid is that it takes the shape of its container. The individual particles in a liquid brush against each other frequently, but otherwise they move about freely. Like a solid, a liquid cannot be compressed to a smaller volume without applying lots of force.
  
  

Gas

• Gas consists of molecules that move very quickly and barely interact with each other. Between each atom or molecule lies plenty of open space. Therefore, a gas can be compressed or expanded with ease. Gas not only takes on the shape of its container, but expands to fill the entire space. The boiling point is the temperature at which liquid matter changes state into a gas.
  
  

Plasma

• According to physicists, nearly all matter in the universe exists as plasma. An extreme high-energy state, plasma composes stars, nebulae and much of interstellar space. The magnetic field around Earth captures plasma streaming away from the sun. In most cases, plasma begins as a superheated gas. The molecules in the gas lose protons and electrons. These loose particles carry loads of energy and move around at high speed. Plasma has exotic characteristics and exhibits behavior similar to both liquids and gases.