Antiparticle

An antiparticle is kind of like the opposite of a normal particle. Normal particles are like little balls, and antiparticles look like the same little balls, only upside down. Some kinds of particles, like protons and electrons, have an antiparticle, which is sometimes called an anti-proton and an anti-electron. An antiparticle has the same mass as the normal particle it is the opposite of, but the opposite electrical charge.