1) Physical quantity 
In classical mechanics, areal velocity (also called sector velocity or sectorial velocity) is the rate at which area is swept out by a particle as it moves along a curve. In the adjoining figure, suppose that a particle moves along the blue curve. At a certain time t, the particle is located at point B, and a short while later, at time t + Δt, th...
a measure of the velocity of one celestial body in orbit about another, equal to the area swept out per unit time by the vector joining the two bodies.