|Definition:|| in the “standard model” of particles, one of six elementary particles combined in triples or in pairs with an antiparticle to constitute other particles|
NOTE 1 The six types of quarks have names (called flavours): down (d), up (u), strange (s), charm (c), bottom (b) and top (t). They are fermions, bearing an electric charge equal to +2/3 or −1/3 elementary charge. Each quark has an antiparticle denoted by overlining its symbol.
NOTE 2 Quarks never occur isolated but only in combination, either in triplets such as neutron, proton or hyperons, or in pairs with antiquarks, as mesons. Quarks are the source of a short-distance strong interaction, which explains in particular the cohesion of atomic nuclei.