P-waves (primary waves) are compressional waves, meaning they cause particles to move back and forth in the same direction as the wave is traveling. The amplitude of a P-wave is the maximum displacement of a particle from its resting position as the wave passes through.

Here's a breakdown:

* Amplitude is measured: in units of distance (e.g., millimeters, centimeters).

* Higher amplitude: indicates a stronger wave, meaning the particles are displaced further from their resting position.

* Lower amplitude: indicates a weaker wave, meaning the particles are displaced less.

However, it's important to note that the amplitude of P-waves is not the only factor that determines the strength of an earthquake. The amount of energy released by an earthquake, which is measured by its magnitude, depends on several factors including the amplitude of the P-waves, the duration of the waves, and the distance from the epicenter.