Wavelength is a property of all waves. It is the distance between a point on one wave, and the same point on the next wave in the sequence.
Wavelength is also a measure of the distance between repetitions of a certain shape feature such as peaks, valleys, or zero-crossings, not a measure of how far any given particle moves.
It is shown in calculations as the lambda symbol (λ), and is defined as λ= Wavespeed/Frequency, whereby the frequency is the number of wave cycles passing a point per unit time.
Within the electromagnetic spectrum: radio waves have the longest wavelength but the lowest frequency; but gamma rays have the shortest wavelength and the highest frequency. All other electromagnetic waves are found between these two extremes of the spectrum.
A good way to remember the order of the electromagnetic spectrum (highest wavelength to lowest wavelength) is through a mnenomic device such as Giant Xylophones Usually Live In Music Rooms (Gamma, X-Ray, Ultra-Violet, Light, Infrared, Radio)
Within Biomedical Sciences wavelength is usually referring to light, and is given the units of nanometres (nm). It is frequently used within spectrophotometry practicals, as certain proteins and compounds are identified by their absorbance of light at specific wavelengths.