CDE is a popular short form for the chemical plasma etching process. Usually the designations "plasma etching" or "chemical etching" address the same etching process.
Chemical Dry Etching in Low pressure plasma is caused by reactions of active species (stimulated atoms, radicals, Ions) with the molecules of the substrate. The process gas must be carefully selected to stimulate the desired reactions (selective etching). The CDE process is isotropic (onidirectional).