In particle physics, the quark (pronounced IPA: /kwɔː(r)k/) is one of the two basic constituents of matter (the other is the lepton). Quarks are the only fundamental particles that interact through all four of the fundamental forces.
Quarks come in six flavors, and their names (up, down, charm, strange, top, and bottom) were also chosen arbitrarily based on the need to name them something that could be easily remembered and used.
Isolated quarks are never found naturally; they are almost always found in groups of two (mesons) or groups of three (baryons) called hadrons. This is a direct consequence of confinement.