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 in reactions, such as those occurring in stars or during particle collisions, the number of baryons and antibaryons before and after the reaction must balance out. This conservation law is important in understanding the behavior of matter in the universe.