In physics and mathematics, amplitude refers to the maximum displacement or distance that an oscillating or vibrating object or wave reaches from its equilibrium position.
For example, in the case of a simple harmonic motion (like a mass attached to a spring), the amplitude is the maximum displacement from the equilibrium position (i.e., the position where the spring is neither compressed nor stretched).
In the case of a wave, such as a sound wave or a light wave, the amplitude is the maximum distance that any part of the wave travels from its resting position (i.e., the position where there is no wave).
The amplitude is usually measured in units of distance, such as meters or feet, or in units of some other physical quantity that is related to distance, such as pressure or electric field strength.