Romanitas is an argued collection of political and cultural concepts and practices by which Ancient Rome is argued to have defined itself.
The word was not common in Roman sources and was first coined late, by the 3rd century AD.
The word, or similar concepts, have been used by various ideologies/movement that argue that their own ideology/movement includes, or should include, the positive aspects of Ancient Rome. In some cases, they may view themselves as the successor or inheritor of ancient Rome.
Examples of stating associations with Ancient Rome include the Holy Roman Empire, the (Roman) Catholic Church, the "Second Rome" (usually referring to Constantinople, the capital of the Byzantine Empire), and the "Third Rome" (various claims, notably Moscow).
In a different sense, concepts such as romanitas may also be used by race denialists, seeing Roman identity as a social construct unrelated to race. See the article on Ancient Rome and the external links there on this.