Definition of 'Amplitude'
The difference in price from the midpoint of a trough to the midpoint of a peak of a security. Amplitude is positive when calculating a bullish retracement (when calculating from trough to peak) and negative when calculating a bearish retracement (when calculating from peak to trough).
Investopedia explains 'Amplitude'
Amplitude is calculated often in technical analysis. For example, it is the amount of retracement in a price and also the width of a channel in a range-bound market.
Chart pattern analysis says that after a retracement, price will continue to move at least a distance equal to the retracement's amplitude.