Quark

An elementary particle that comes in six flavours: up, charm and top (all with +2/3 electrical charge) and down, strange and bottom (all with -1/3 electrical charge). Quarks also have a property known as “colour charge” and cannot exist freely because of a phenomenon called “colour confinement”: they are held together by gluons to form hadrons.

Links: Read more on Wikipedia

See also: Hadron Proton Jet Gluon