A nomen oblitum (Latin for "forgotten name") is a technical term, used in zoological nomenclature, for a particular kind of disused scientific name.
In its present meaning, the nomen oblitum came into being with the fourth, 1999, edition of the International Code of Zoological Nomenclature. After 1 January 2000, a scientific name may be formally declared to be a nomen oblitum when it has not been used as a valid name within the scientific community since 1899, and when it is either a senior synonym (there is also a more recent name which applies to the same taxon, and which is in common use) or a homonym (it is spelled the same as another name, which is in common use). Once it has formally been declared to be a nomen oblitum, the disused name is to be 'forgotten'. By the same act, the junior name must be declared to be a nomen protectum; from then on, it takes precedence.
In the first and second editions of the Zoological Code (valid between 6 November 1961 and 1 January 1973), the term was also used, but names then indicated as such do not have the same status. Notable examples of this previous use are: