Quarks are the building blocks of all the particles of matter except the leptons. They form the well known proton and neutron, and a host of other short- lived particles that have been discovered during the past 50 years.
Protons are baryons, formed by two up and one down quark.
The kaon is another meson. A kaon always contains a strange quark or antiquark, and it has half a proton's mass.