In physics, a rare form of subatomic matter that is a mirror image of normal matter. The antiparticle corresponding to an elementary particle has the same mass as the particle but is opposite in all other properties. The antiparticle corresponding to an electron is a positron, which has the same mass as an electron but a positive charge. Antiprotons have the same mass as protons but a negative charge. When matter and antimatter come together, the two particles annihilate each other, converting their mass into energy or into other types of particles.
Note: As far as scientists can tell, there is almost no naturally occurring antimatter in the universe, although it is possible to make antimatter in particle accelerators.