A subatomic particle composed of a quark and an anti-quark. Not seen under everyday conditions, but produced at high temperatures or in reactions between atoms.
An unstable nuclear particle with a rest mass between that of an electron and a proton. Also known as the pi meson.
A pion is a strongly interacting elementary particle of spin 0 having a rest mass roughly 270 times that of the electron. It exists in neutral, positive, and negative charged states.