In high energy physics, B-L (pronounced bee minus ell) is the baryon number minus the lepton number. This is the charge of a global /gauge U(1) symmetry in some some GUT models, called U(1)_B-L. Unlike baryon number alone or lepton number alone, this hypothetical symmetry is not broken by chiral anomalies or gravitational anomalies, which is why this symmetry is often invoked.