Angular momentum is the component of momentum due to rotation. Angular momentum must be specified relative to a center of rotation. Angular momentum describes the rotational motion of the vector from o to x due to the motion at x (p). In other words, the fraction of x's momentum rotating around o. This rotational motion will be about an axis perpendicular to both the vector and p. The angular momentum captures this axis of rotation (centered at o).

The time derivative of angular momentum is called torque.