Wiktionary
n. (context physics English) A quantum number related to the difference between the numbers of quarks and antiquarks in a system of subatomic particles
WordNet
n. a number equal to the difference between the number of baryons and the number of antibaryons in any subatomic structure; it is conserved in all types of particle interactions
Wikipedia
In particle physics, the baryon number is a strictly conserved additive quantum number of a system. It is defined as
$B = \frac{1}{3}\left(n_\text{q} - n_\bar{\text{q}}\right),$where n is the number of quarks, and n is the number of antiquarks. Baryons (three quarks) have a baryon number of +1, mesons (one quark, one antiquark) have a baryon number of 0, and antibaryons (three antiquarks) have a baryon number of −1. Exotic hadrons like pentaquarks (four quarks, one antiquark) and tetraquarks (two quarks, two antiquarks) are also classified as baryons and mesons depending on their baryon number.
Usage examples of "baryon number".
It is well known, is it not, that decay of the proton would violate the law of conservation of baryon number.