Serbo-Croatian or Croato-Serbian (also Croatian or Serbian, Serbian or Croatian), is a South Slavic diasystem. "Serbo-Croatian" was used as as an umbrella term (dachsprache) for dialects spoken in Serbia, Croatia, Montenegro, Bosnia and Herzegovina; it was one of the official languages of Yugoslavia from 1918 to 1991 (along with Slovenian and Macedonian). In its standardized form, it was based on Štokavian dialect and defined in Ekavian and Iyekavian variants called "pronounciations" (unofficially, there were "Eastern" (based on Serbian idiom) and "Western" (based on Croatian idiom) variants. By extension, it often declared also Kaykavian and Chakavian as its dialects (while Torlakian dialect was never recognized in official linguistics), but they were not in official use. The term was mentioned for the first time by Slovenian philologist Jernej Kopitar in a letter from 1836, although it cannot be ruled out that he had become acquainted with the term by reading the Slovak philologist Pavol Jozef Šafárik's manuscript "Slovanské starožitnosti" printed 1837.
With the breakup of Yugoslavia in the 1990s, its languages followed suit and Croatian, Serbian, Bosnian (Ausbausprachen). Currently there is a movement to create a Montenegrin language, separate from Serbian. Conversely, the complex term "Serbo-Croatian" declined in usage, first from official documents and gradually from linguistic literature. Today, the name Serbo-Croatian is a controversial issue due to history, politics, and the variable meaning of the word language. Many native speakers nowadays find the term politically incorrect or even insulting. Others, however, continue using the original language name, as they have studied it at school; also recently the traditional Serbo-Croatian persisted as an important lingua franca of mutual understanding across West Balkans.
Linguists are divided on questions regarding whether the name is deprecated. It is still used, for lack of a more succinct alternative, to denote the "daughter" languages as a collectivity. An alternative name has emerged in official use abroad — Bosnian/Croatian/Serbian (BHS). It is also known in the regional linguistic community as the Central South Slavic diasystem.
Mutually intelligible forms of it continue to be used under different names and standards in today’s Serbia, Montenegro, Croatia, and Bosnia and Herzegovina, and are still reasonably well understood in Republic of Macedonia and Slovenia. Whilst most in the latter two countries born before 1982 will be fluent in the language, younger people grown after their independence have had more limited contact with it, mostly through regional media.