Antimatter

every particle (matter) has corresponding antiparticle
        (antimatter)

antiparticles are same as corresponding matter particle,
       except for all charges opposite
       proton is electrically positive; anti-proton is
              electrically negative
       both have exactly same mass
       affected in the same way by gravity

when particle and its antiparticle meet,
       annihilate into pure energy

energy may materialize
       into any particle / anti-particle pair,
       or into neutral force-carrier particles

       such as photons; W, Z bosons, or gluons