Glossary entry

suppression, n. (suppress, v.)
A ruling by the Commission, using its plenary power,
(1) that a work is to be deemed, for nomenclatural purposes, as unpublished, or that names and acts in it are not available; or
(2) that an available name is never to be used as valid because (a) it is available only for the purpose of homonymy ("partial suppression") or (b) it is not available for the purposes of priority and homonymy ("total suppression"; but a totally suppressed species-group name may still denote the type species of a nominal genus or subgenus [Art. 81.2.1]); or
(3) that an available name is only to be used as valid under stated conditions (e.g. when not considered a synonym of a particular later name) ("conditional suppression").

Source:
International Commission on Zoological Nomenclature (1999) International Code of Zoological Nomenclature. Fourth Edition. - International Trust for Zoological Nomenclature, XXIX + 306 pp.