Wavelength is measured in meters or other units of length such as centimeters or millimeters. A wavelength denotes the length of a wave from either crest to crest or trough to trough.
A crest is the highest point of the wavelength curve, and the trough is the lowest point of the wavelength curve. A wave can be measured using frequency because the higher the frequency of the signal, the shorter the wavelength. As wavelength is inversely related to frequency, another way to measure the wavelength is to divide the frequency of the waves (oscillations) by the speed of the wave, in so far that wavelength equals speed/frequency.