A wave's wavenumber (or spatial frequency) is the reciprocal of its wavelength, the number of cycles per unit distance, a convenient quantity in the analysis and modeling of waves including EMR and sound waves. An example unit is 1/cm, which means "number of complete waves in a cm" (or "fraction of a complete wave that spans a cm"). If you viewed the ocean and noticed that at some instant, over a distance of 10 meters, there were three waves, you could cite the average wavenumber as 0.3 1/m. Pattern regarding wave terms:
(the wave period or period being the length of time it takes one cycle of the wave to pass.) Relations between the terms (given compatible base units, e.g., m and 1/m):
wavelength × wavenumber = 1 frequency × period = 1 wavelength × frequency = wave speed For EMR: wavelength × frequency = c
The symbol ν is sometimes used for the wavenumber, but also often for frequency. Sometimes, for wavenumbers, a tilda (~) is placed over ν to distinguish it.
The angular wavenumber is 2π × the wavenumber.