For a name to be available, in addition to meeting certain criteria for publication, there are a number of general requirements it must fulfill: it must include a description or definition of the taxon, must use only the Latin alphabet, must be formulated within the binomial nomenclature framework, must be newly-proposed (not a redescription under the same name of a taxon previously made available) and originally used as a valid name rather than as a synonym, must not be for a hybrid or hypothetical taxon, must not be for a taxon below the rank of subspecies, etc.
This hierarchical system of typification provides a concrete empirical anchor for all zoological names.
Despite the frequent confusion caused by common sense, an unavailable name is not necessarily a nomen nudum.
A good examplification of this is the case of the unavailable dinosaur name "Ubirajara jubatus", which was assumed by common sense to be a nomen nudum before a detailed analysis of its nomenclatural status.
[2] Under the International Code of Nomenclature for algae, fungi, and plants, this term is not used.