Waveguide dispersion
That part of the chromatic dispersion resulting from the different speeds at which light travels in the core and cladding of a single mode fibre. For the most part this deals with the fibre as a waveguide structure.

Wavelength
A measure of the color of the light for which the performance of the fiber has been optimized. It is a length
stated in nanometers (nm) or in micrometers (um).

Wavelength-Devision Multiplexer (MUX)
A branching device with two or more input ports and one output port where the light in each input port is restricted to a preselected wavelength range, and the output is the combination of the light from the input ports.

Wavelength-Division Demultiplexer (DEMUX)
A branching device which performs the inverse operation of a wavelength-division multiplexer, where the input is an optical signal comprising two or more wavelength ranges and the output of each port is a different preselected wavelength range.

WDM
Wavelength Division Multiplexer: Multiplexing of signals by sending them at different wavelengths through the same fibre.