. "In particle physics, a pion (or a pi meson, denoted with the Greek letter pi: \u03C0) is any of three subatomic particles: \u03C00, \u03C0+, and \u03C0\u2212. Each pion consists of a quark and an antiquark and is therefore a meson. Pions are the lightest mesons (and, more generally, the lightest hadrons), because they are composed of the lightest quarks (the u and d quarks)."@en . .