Baryon number conservation is a fundamental principle in particle physics stating that the total baryon number in a closed system remains constant over time. The baryon number is defined as the number of baryons (such as protons and neutrons) minus the number of antibaryons. This means that during any particle interaction or decay, the sum of baryons and antibaryons before and after the event must be the same. This conservation law is crucial for understanding processes in nuclear reactions and the behavior of particles in the universe. It helps explain why certain reactions, like those involving neutrinos or quarks, do not change the overall baryon count, ensuring stability in atomic structures and the formation of matter.