A proton is a subatomic particle and a baryon, which resides within the atomic nucleus alongside neutrons. It carries a positive electrical charge, equivalent in magnitude to the elementary charge, making it fundamental to the structure of matter. The particle is composed of fundamental constituents called quarks, specifically two up quarks and one down quark, which are held together by the strong nuclear force. This positive charge is crucial, as the relative balance of positive charge (protons) and negative charge (electrons) defines the atomic element, while the protons themselves determine the atomic number and the identity of the element.