Amplitude is the maximum displacement of a particle in a wave from its equilibrium position. It essentially measures how "big" the wave is.

Here's a breakdown:

* Equilibrium Position: The resting position of the particle when no wave is present.

* Displacement: The distance a particle moves from its equilibrium position.

* Amplitude: The maximum displacement, either above or below the equilibrium position.

Think of a wave on a string. The amplitude is how far the string moves up or down from its straight, resting position.