Final answer:
The resting position or center line of a wave is known as the equilibrium position, which is distinct from the points of maximum displacement, the crests and troughs, characterized by the amplitude of the wave.
Step-by-step explanation:
The point at which a wave is in the resting position or reaches the center line is called the equilibrium position. Unlike the maximum deformation points, such as the crests or troughs, the equilibrium position is where the medium through which the wave is traveling would be if it were undisturbed. When discussing waves, it's important to understand that the amplitude of the wave represents the maximum displacement from this equilibrium position. Crests are at a distance of +A (positive amplitude) above the equilibrium position, while troughs are at a distance of -A (negative amplitude) below it. Hence, the amplitude (A) is the characteristic height of the wave above or below the equilibrium position.