Definition of "quark"

quark¹

/kwɔːk/

noun
plural quarks
1. (physics) In the Standard Model, an elementary subatomic particle that forms matter. They combine to form hadrons, such as protons and neutrons.
  Quotations
  There were also particles no one had predicted that just appeared. Five of them […, i]n order of increasing modernity, […] are the neutrino, the pi meson, the antiproton, the quark and the Higgs boson.
  2012 March-April, Jeremy Bernstein, “A Palette of Particles”, in American Scientist‎, volume 100, number 2, page 146
2. (computing, X Window System) An integer that uniquely identifies a text string.
  Quotations
  Two functions are provided to convert between strings and quarks: XrmStringToQuark and XrmQuarkToString […]
  2012, Keith D. Gregory, Programming with Motif, page 453

quark²

noun
uncountable
1. A soft creamy cheese, eaten throughout northern, central, eastern, and southeastern Europe as well as the Low Countries, very similar to cottage cheese except that it is usually not made with rennet.

quark³

noun
plural quarks
1. (Falkland Islands, informal) The black-crowned night heron, Nycticorax nycticorax.