Pronunciation: (kwôrk, kwärk),[key] —n. Physics.any of the hypothetical particles with spin 1/2, baryon number 1/3, and electric charge 1/3 or -2/3 that, together with their antiparticles, are believed to constitute all the elementary particles classed as baryons and mesons; they are distinguished by their flavors, designated as up (u), down (d), strange (s), charm (c), bottom or beauty (b), and top or truth (t), and their colors, red, green, and blue. Cf. color (def. 18), flavor (def. 5), quantum chromodynamics, quark model.