Matter is the general term for all physical substances. It consists at the basic level from charged subatomic particles. There is also a variant of matter where the particles have the same mass and configuration, but an opposite charge: antimatter. These variants react heavily with each other, canceling each other out in a matter-antimatter reaction. This kind of reaction was widely used to propel starships.
Matter exists in four fundamental states that exhibit differing physical properties.
The following are the states of matter in order of increasing kinetic energy (temperature):
Solids exhibit strong intermolecular bonds that maintain a fixed shape and volume. The intermolecular bonds in a liquid are partially counteracted by the average thermal energy of the individual atoms in the substance, thereby giving the liquid its fluidic properties. Where solids retain both shape and volume, the fluidic properties of liquids allow them to change their shape to fit their container, but they remain non-compressible, maintaining constant volume. In a gas, the bonds are completely overcome by thermal energy. Gases exhibit fluidic properties but unlike liquid, they are compressible. In a plasma, the thermal energy is so high that most of the atoms break apart and ionize into free electrons and cations.
Both matter and antimatter can exist in these phases.
Matter is naturally created at the creation point at the galactic core, creating matter-energy whirlwinds which are capable of transporting objects into an alternate universe where the world of Megas-Tu exists. (TAS: "The Magicks of Megas-Tu")