"In particle physics, a pion (short for pi meson, denoted with π) is any of
three subatomic particles: π0, π+, and π−. Pions are the lightest mesons and they play an important role in explaining the low-energy properties of the strong nuclear force."
"Pions are mesons with zero spin, and they are composed of first-generation quarks. In the quark model, an up quark and an anti-down quark make up a π+, whereas a down quark and an anti-up quark make up the π−, and these are the antiparticles of one another. The uncharged pions are combinations of an up quark with an anti-up quark or a down quark with an anti-down quark, have identical quantum numbers, and hence they are only found in superpositions. The lowest-energy superposition of these is the π0, which is its own antiparticle. Together, the pions form a triplet of isospin. Each pion has isospin (I = 1) and third-component isospin equal to its charge (Iz = +1, 0 or −1)."