A quark ( or ) is an elementary particle and a fundamental constituent of matter. Quarks combine to form composite particles called hadrons, the most stable of which are protons and neutrons, the components of atomic nuclei. Due to a phenomenon known as color confinement, quarks are never directly observed or found in isolation; they can be found only within hadrons, such as baryons (of which protons and neutrons are examples), and mesons. For this reason, much of what is known about quarks has been drawn from observations of the hadrons themselves.

QuArK (aka Quake Army Knife), is a free and open source program for developing 3D assets for a large variety of video games, mostly first-person shooters using engines similar to or based on the Quake engine by id Software. QuArK runs on Microsoft Windows.