Protons Stable elementary particles having the smallest known positive charge, found in the nuclei of all elements. The proton mass is less than that of a neutron. A proton is the nucleus of the light hydrogen atom, i.e., the hydrogen ion.
[1. Abbreviation for pupil; optic papilla.2. In polynucleotide symbolism, phosphoric ester or phosphate.3. Symbol for pico-2; the negative decadic logarithm; proton; protein; momentum (in italics).4. In cytogenetics, symbol for the short arm of a chromosome.