A quark is one of two currently recognized groups of fundamental particles, which are subatomic, indivisible (at least as far as we know today) particles that represent the smallest known units of matter . Twelve fundamental particles - six quarks and six leptons (the other type) - are the basic building blocks for everything in the universe.
Both quarks and leptons are distinguished in terms of flavors . as a way to distinguish them from each other. The six quark flavors are: up, down, top, bottom, strange, and charm. Everything in our readily observable world seems to be made up of just the up quark, the down quark, and the electron (which is the most famous flavor of lepton).
Murray Gell-Mann named the quark in 1964. Independently of each other, Gell-Mann and another physicist, George Zweig, theorized that the differences between protons, neutrons, and newly discovered particles could be explained by the existence of these still smaller particles. Gell-Mann won the 1969 Nobel Prize in physics for his work with fundamental particles.
It is entirely possible that quarks and leptons may turn out to be made up of smaller particles. The atom , after all, was once thought to be the smallest possible unit of matter. However, as we now know, the nuclei of atoms are made up of protons and neutrons which are, in turn, made up of quarks and leptons.