The proton is positively charged, subatomic particle located in the nucleus of an atom. It constitutes the nucleus together with the neutron, which changes continuously by the emission and absorption of pions.

Quark model of the proton.

As formed by quarks the proton belongs to the family of hadrons and in particular to the group of baryons. Having semi-integer spin is a fermion.

The proton has 1836 times the mass of the electron, but precisely the same size charge \((e= 1.602\times 10^{-19}\;\textrm{C})\), only positive rather than negative.