noun

• (particle physics) In the Standard Model, one of a number of elementary subatomic particles having fractional electric charge that forms matter. They are theorized not to exist in isolation, but only in combinations in hadrons such as neutrons and protons or in quark–gluon plasmas.
  "A simpler and more elegant scheme can be constructed if we allow non-integral values for the charges. We can dispense entirely with the basic baryon b if we assign to the triplet t the following properties: spin #92;frac#123;1#125;#123;2#125;, z#61;#123;-#92;frac#123;1#125;#123;3"
• (by extension, computing, X Window System)
  "Two functions are provided to convert between strings and quarks: XrmStringToQuark and XrmQuarkToString […] The second takes a quark as its parameter and returns a pointer to its associated string; it is used primarily for debugging and runtime error messages."
• (by extension, computing, X Window System)

noun

• (Falkland Islands, informal) The black-crowned night heron (Nycticorax nycticorax).