An undesired Mode that is confined to the Cladding of an optical Fiber by virtue of the fact that the cladding has a higher Refractive Index than the surrounding medium, i.e., air or Primary polymer overcoat.

Note: Modern fibers have a primary polymer overcoat with a Refractive Index that is slightly higher, rather than lower, than that of the cladding, in order to strip off cladding Modes after only a few centimeters of propagation.