Wavelength Services - (May be associated with Wave Division Multiplex, WDM) - Wavelength Services are dedicated, protected wavelengths from a service provider for the exclusive use of a customer. Wavelength Division Multiplexing (WDM) is service or the sale of discrete wavelengths on a fiber transport facility. WDM transmits multiple wavelengths over a single optical fiber, each data signal using its own wavelength (color band). Wavelength services often are protocol independent.

Wavelength-division Multiplexing - (WDM) - A technology in fibre-optic communications.  WDM is a scheme for transmitting two or more separate signals over a single fiber optic cable by using a separate wavelength (color) for each signal.
wikipedia.org/wiki/Wavelength_division_multiplexing

Frequency-division Multiplexing - (FDM)
-  wikipedia.org/wiki/Frequency-division_multiplexing