A meson is composed of a quark, and an antiquark, and binding gluons.
An example is a pion of charge +1 (
+),
which is made up of an up quark and anti-down quark.
The antiparticle of a meson is the quark and the antiquark
reversed. For example the anti-particle of
+ is
-,
which is made of a down quark and an anti-up quark.
A meson is a color-neutral object, since its quark and antiquark have opposite color charges. Thus, a meson can be found in isolation. All mesons are unstable.
Since a meson has an integer spin, it is a boson. The spin is made of the spins of the quarks, plus a contribution from their motion around each other. For example notice that a pion and a rho have the same quarks, but different spins and masses.
spin=0, mass=0.14 GeV/c^2
spin=1, mass =0.770 GeV/c^2