quantum: (See also classical; mechanics, quantum; and field theory, quantum)

quantum chromodynamics (QCD): (See also the strong interaction)

quantum electrodynamics (QED): (See also the electromagnetic interaction)

quark: Quarks are the particles which, when bound together form a hadron. By "bound", I mean in the same sense that protons and neutrons are bound to form the nucleus of an atom, and that bound atoms form molecules. The quarks are bound due to their reactions under the strong interaction much like the moon is bound to the Earth by gravity, like the Earth is bound to the sun by gravity, and like the electrons of an atom are bound to the nucleus of the atom by electromagnetism. There are currently six known quarks. They are distinguished by a property referred to as flavor. Each of these "flavors" of quark can have one of three "color charges".

quark, constituent:

quark, family of: Quarks can be divided into families in different ways. They are usually grouped in the following way: the lightest family is comprised of the u and d quarks and their anti-particles. The next heavier family is comprised of the s and c quarks with their anti-particles. The heaviest known quark family is comprised of the b and t quarks with their anti-particles.

quark flavor: There are six different types of quarks, each with a different mass. When quarks were first discovered, it was thought that the type of quark determined how they interacted (see charge). This would be an important property, so the type of quark was called its "flavor." It later turned out that these flavors are merely types of quarks. It is the color charge of the quark which determines how it reacts to the strong interaction. The flavor (type) of a quark does determine how it reacts to the weak interaction, but this only determines what it can decay (i.e. change) into. The quark flavors are up, down, strange, charm, bottom, and top.