High Quality Content by WIKIPEDIA articles! A waveguide is a structure which guides waves, such as electromagnetic waves or sound waves. THere are different types of waveguide for each type of wave. THe original and most common meaning is a hollow metal pipe used for this purpose. WAveguides differ in their geometry which can confine energy in one dimension such as in slab waveguides or two dimensions as in fiber or channel waveguides. IN addition, different waveguides are needed to guide different frequencies: an optical fiber guiding light. AS a rule of thumb, the width of a waveguide needs to be of the same order of magnitude as the wavelength of the guided wave.