What is "nomen novum"

In biological nomenclature, a nomen novum ( Latin for "new name"), new replacement name (or replacement name, new substitute name, substitute name) is a technical term. It indicates a scientific name that is created specifically to replace another scientific name, but only when this other name can not be used for technical, nomenclatural reasons (for example because it is a homonym: it is spelled the same as an existing, older name); it does not apply when a name is changed for taxonomic reasons (representing a change in scientific insight). It is frequently abbreviated, e.g. nomen nov., nom. nov., or more explicitly by the rank specified, e.g. superordo nov.