Central force
A force directed along the line connecting two bodies, depending only on their separation. Gravity and Coulomb attraction both qualify.
Definition
A central force acts along the line joining two objects and depends only on the distance between them — not on the angle, not on their velocities, not on any internal state. Gravitational attraction between point masses and the Coulomb force between point charges are the canonical examples.
Central forces have a beautiful structural consequence: angular momentum about the force centre is conserved. Because the force points directly at the centre, its moment arm is zero, its torque is zero, and dL/dt = 0. Kepler's second law — planets sweep out equal areas in equal times — is exactly this fact, written a century before Newton explained it.