Final answer:
The term 'wavelength' refers to the distance between successive peaks or any two consecutive points in phase on an electromagnetic wave.
Step-by-step explanation:
The distance between successive peaks of an electromagnetic wave is known as the wavelength. It is represented by the lowercase Greek letter lambda, 'λ'.
The wavelength is measured in meters and is fundamentally important in understanding the properties of electromagnetic waves, such as light and radio waves. This distance can be observed between two consecutive points that are in phase with each other; typically, these points are the crests (peaks) or the troughs (valleys) of the wave.
In answering the student's question, the correct term that fills in the blank is 'wavelength'.