Definitions for up quark
Random House Webster's College Dictionary
the quark having electric charge ? times the electron's charge and together with the down quark being a constituent of nucleons.
Origin of up quark:
a stable quark with an electric charge of +2/3 and a mass 607 times that of an electron
A quark having a fractional electric charge of +2/3 and a mass of about 1.5 to 4 MeV. Symbol: u