quark Any one of six particles (although there is increasing evidence of another two) and their antiparticles (antiquarks) that are the constituents of the hadron group of elementary particles. They occur in one of six ‘flavours’: up, down, top, bottom, charmed, and strange. Antiquarks have similar flavours but their charge is opposite that of their corresponding quark. Quarks always exist in combination; free quarks cannot exist. A baryon, such as a proton or neutron, consists of three.

quark¹ / kwärk/ • n. Physics any of a number of subatomic particles carrying a fractional electric charge, postulated as building blocks of the hadrons. Quarks have not been directly observed, but theoretical predictions based on their existence have been confirmed experimentally.quark² • n. a type of low-fat curd cheese.

quark in physics, any of a number of subatomic particles carrying a fractional electric charge, postulated as building blocks of the hadrons. Quarks have not been directly observed but theoretical predictions based on their existence have been confirmed experimentally. The name (originally quork) was invented in the 1960s by Murray Gell-Mann; it was changed by association with the line ‘Three quarks for Muster Mark’ in Joyce's Finnegans Wake (1939).

quark (quarg) Originally German; very low‐fat cheese made from skim milk; contains 80% water; a 100‐g portion is a good source of protein and vitamin B₁₂, a source of vitamin B₂, with only a trace of fat, contains 40 mg of sodium and 90 mg of calcium and supplies 80 kcal (325  kJ).