An up quark is a fundamental particle and one of the building blocks of matter. It is a type of quark, which are elementary particles that combine to form protons and neutrons, the components of atomic nuclei. The up quark has a positive electric charge of +2/3e and is one of the lightest quarks, with a mass of about 2.3 MeV/c². Up quarks combine with down quarks to form protons and neutrons. For example, a proton consists of two up quarks and one down quark, while a neutron is made of one up quark and two down quarks. These combinations are essential for the structure of atoms and the existence of matter in the universe, making up the atomic nuclei.