amplitude

Amount of a waveform's deviation from center. When used to describe sound, amplitude means volume. (Friend, David, Learning Music with Synthesizers)

The difference between 0 and maximum or minimum changes of polarity within a wave or cycle.

The magnitude of periodic dynamic motion (vibration). Amplitude is measured in terms of peak-to-peak, zero-to-peak, rms, or average. (Field of Rotating Machinery Measurment, Monitoring and Analysis, Bentley Nevada Corporation)

Amplitude refers to the strength, or loudness, of a sound, or of the strength of an electrical signal representing sound. If the sound or signal is represented as a wave pattern on an oscilloscope or graph, the amplitude corresponds to the height of the wave (i.e., the magnitude of the swing in each cycle). (Fantel, Hans, The True Sound of Music - A Practical Guide to Sound Equipment for the Home)

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