Bottomness
In physics, bottomness (symbol B′ using a prime as plain B is used already for baryon number) or beauty is a flavour quantum number reflecting the difference between the number of bottom antiquarks (n) and the number of bottom quarks (n) that are present in a particle:

Bottom quarks have (by convention) a bottomness of −1 while bottom antiquarks have a bottomness of +1. The convention is that the flavour quantum number sign for the quark is the same as the sign of the electric charge (symbol Q) of that quark (in this case, Q = −). As with other flavour-related quantum numbers, bottomness is preserved under strong and electromagnetic interactions, but not under weak interactions. For first-order weak reactions, it holds that . This term is rarely used. Most physicists simply refer to "the number of bottom quarks" and "the number of bottom antiquarks". References
 

Quarks
Flavour (particle physics)