A proton is one of the fundamental subatomic particles, along with neutrons and electrons. It is found in the nucleus of an atom and carries a positive electric charge, equal in magnitude to the negative charge of an electron. The number of protons in the nucleus of an atom determines what element it is, as each element has a unique number of protons. The mass of a proton is approximately 1.007 atomic mass units and it is believed to be composed of even smaller particles called quarks. Protons are essential to the stability of atomic structure and play crucial roles in nuclear reactions and chemistry.