Proton has several meanings:

• Proton in physics is a subatomic particle with a positive fundamental electric charge of 1.6 × 10^-19 coulomb and a mass of 938 MeV (1.6726231 × 10^-27 kg, or about 1836 times that of an electron).
• Proton in chemistry is the H⁺ (positively charged hydrogen) ion, because an ordinary hydrogen atom is one electron orbiting a nucleus which is composed only of one proton, and in the ion that electron is lost.
• Proton (formal designation: UR-500) is a Soviet unmanned space vehicle design first launched in 1965 and still in use as of 2003.
• Proton was a Soviet artificial satellite.
• Proton is a type of Russian diver propulsion vehicle: see Protei-5 Russian diver-rider.
• Proton (short for Perusahaan Otomobil Nasional, meaning National Car Project) is a Malaysian car manufacturer initiated in 1983 by Prime Minister Mahathir Mohamad. The main plant is located in Shah Alam.
• Proton in geology is a province of a craton (an ancient section of continental crust) that is between 1.6 and 2.5 billion years old.
• Proton E-Purse is a Belgian smartcard system for low-value payments.
• Proton is the name for a renal/clinical database developed by CCL (Clinical Computing Limited).
• Distinguish from Proto.