Mesons are hadrons, which simply means that they are made of quarks. Since quarks have different fractional charges, mesons can have a charge. However, the charges of the quarks may cancel out, forming an uncharged meson. The rest of the hadron family are known as baryons, which are made of three quarks. Since quarks all have a spin of 1/2, three of them will never add up to an integer spin. An integer spin is simply 0, 1, or 2. Particles with an integer spin are called bosons, which obey Bose-Einstein Statistics. This means that more than one boson can actually be in the same point in space at the same time. However, a meson is made of one quark and one antiquark, which each do not have an integer spin. Particles which do not have an integer spin have a spin of 1/2 or 3/2. These particles with 1/2 spin are called Fermions because they obey Fermi-Dirac Statistics. This means that no more than one fermion can be in the same point in space at the same time. All known baryons and quarks (and antiquarks) are fermions, and all mesons are bosons. This can get very confusing because this means that more than one meson can exist in the same point in space at the same time, but the quarks that make up mesons cannot exist in the same point in space at the same time.