Final answer:
The measurement of the vertical size of the waveform is called its amplitude, which is the height above or below the equilibrium position and is crucial for determining the wave's energy.
Step-by-step explanation:
The measurement of the vertical size of the waveform is known as its amplitude. The amplitude is the characteristic height of the wave above or below the equilibrium position, typically measured in meters (m). This measurement is crucial as it determines the energy of the waveform; a higher amplitude indicates a greater amount of energy. The amplitude is symbolized by the letter 'A' and is defined as half the distance from the peak to the trough of a wave. Also, the waveform's speed and energy are directly influenced by both its amplitude and frequency, with the wave speed being the product of its wavelength (lambda, λ) and frequency (f).