Antiparticle (Physics Dictionary)

Antiparticle: In particle physics, every type of particle has an associated antiparticle with the same mass but with opposite physical charges such as electric charge. For example, the antiparticle of the electron is the antielectron (which is often referred to as the positron). While the electron has a negative electric charge, the positron has a positive electric charge, and is produced naturally in certain types of radioactive decay. Some particles, such as the photon, are their own antiparticle. Otherwise, for each pair of antiparticle partners, one is designated as “normal” matter (the kind comprising all matter with which humans usually interact), and the other (usually given the prefix “anti-“) as antimatter.