A binary operator representing multiplication, composition of functions, or group actions in abstract algebra and category theory.
Examples
Group operation notation
(G, \bullet) \text{ is a group under the operation } \bullet
Bullet product in vector calculus
\vec{F} \bullet \vec{G} = F_x G_x + F_y G_y + F_z G_z
Composition of morphisms in category theory
f \bullet g = h \text{ where } f: Y \to Z \text{ and } g: X \to Y