Citation:
Density refers to how closely packed or crowded something is within a given area or volume. In calculus, it can refer to how closely spaced the slope field lines are in relation to each other.
How quickly one quantity changes in relation to another over time.
Gradient Vector Field: A vector field that represents both magnitude and direction at each point on its domain.
Level Curve/Contour Line: A curve on which all points have equal values for some given function.