- the quark having electric charge −1/3 times the elementary charge and bottom quantum number −1. It is more massive than the up, down, strange, and charmed quarks.
- A quark with a charge of -13. Its mass is smaller than that of the top quark, but larger than that of all the other quarks. The bottom quark is sometimes referred to as the beauty quark, though this term is falling out of use. See Table at subatomic particle.