Baryon number is a quantum number that represents the total number of baryons in a system. Baryons are a type of subatomic particle, which include protons and neutrons, that are made up of three quarks. Each baryon has a baryon number of +1, while antibaryons, which are their counterparts, have a baryon number of -1. Other particles, like mesons and leptons, have a baryon number of 0. In any physical process, the total baryon number must remain constant, a principle known as baryon number conservation. This means that if a reaction produces baryons, it must also produce an equal number of antibaryons to balance the baryon number. This conservation law is important in understanding various phenomena in particle physics and cosmology, including the behavior of nuclear reactions and the early universe.