Definition of antimatter (antiparticle)

1) Species of subatomic particles that have the same mass and spin as normal particles, however, they have opposite electrical charges from their normal matter counterparts. In the case of antineutrons they are opposite of neutrons in magnetic moment. Positrons, which are the counterpart to electrons, have a positive charge and antiprotons have a negative charge. Photons are their own antimatter counterpart. When a particle of matter collides with a particle of antimatter, both particles are destroyed and their masses are converted to photons of equivalent energy.