The term Vlach is originally an exonym. All the Vlach groups used various words derived from romanus to refer to themselves: Români, Rumâni, Rumâri, Aromâni, Arumâni etc. (note: the Megleno-Romanians nowadays call themselves "Vlaşi", but historically called themselves "Rămâni"; The Istro-Romanians also have adopted the names Vlaşi, but still use Rumâni and Rumâri to refer to themselves).
The Vlachs are generally considered descendants of Romanised indigenous ancient(Paleo-Balkanic) peoples such as the Thracians (incl. Dacians) and Illyrians, as well as other populations of the Balkans such as Greeks (Hellenes and Greco-Romans).
The Vlach languages, also called the Eastern Romance languages, have a common origin from the Proto-Romanian language. Over the centuries, the Vlachs split into various Vlach groups (see Romania in the Dark Ages) and mixed with neighbouring populations: Slavs, Greeks, Albanians, Cumans, and others. (Almost all modern nations in Central and Southeastern Europe have native Vlach minorities: Hungary, Ukraine, Serbia, Croatia, Macedonia, Albania, Bosnia, Greece and Bulgaria. In other countries, the native Vlach population have been completely assimilated by the Slavic population and therefore ceased to exist: Poland, Czech Republic, Slovakia and Montenegro. Only in Romania and the Republic of Eastern Moldova, the Vlach (Dacoromanian or Romanian proper) population consist an ethnic majority today.
The word Vlach is ultimately of Germanic origin, from the word Walha, a name used by ancient Germanic peoples to refer to (mainly) Romance-speaking neighbours. As such, it shares its history with several ethnic names all across Europe, including the Welsh and Walloons. Slavic people initially used the name Vlachs when referring to Romanic people in general. Later on, the meaning became narrower or just different. For example Italy is called Włochy in Polish, and Olaszország ("Olasz country") in Hungarian.
Through history, the term "Vlach" was often used for groups which were not ethnically Vlachs, often pejoratively - for example for any shepherding community, or for Christians by Muslims (Karadjaovalides). In the Croatian region of Dalmatia, Vlaj/Vlah (sing.) and Vlaji/Vlasi (plural) are the terms used by the inhabitants of coastal towns for the people who live inland or pejoratively: barbarians who came from the mountain. In Greece, the word Βλάχος (Vláhos) is often used as a slur against any supposedly uncouth or uncultured person, but literally it simply means countryperson and is often used as a synonym for Χωριάτης (Choriátis) which means villager.
Besides the separation of some groups (Aromanians, Megleno-Romanians) during the Age of Migration, many other vlachs could be found all over the Balkans, as far north as Poland and as far west as the regions of Moravia (part of the modern Czech Republic), and the present-day Croatia where the Orthodox Vlachs took Serb identity, while the Catholic Vlachs took Croat national identity . They reached these regions in search of better pastures, and were called "Wallachians" ("Vlasi; Valaši") by the Slavic peoples.
Vlachs have a similar genetic structure compared to other southeastern Europeans. Population genetics analyses have demonstrated significant molecular variance among different Vlach groups, suggesting that they do not constitute a homogeneous group. Instead, most of the tested Vlach groups were genetically similar to their Greek and Slavic-speaking neighbours. (to be verified)
Bosch et al. attempted to analyze whether Vlachs are the descendents of Latinized Dacians, Illyrians, Thracians, Greeks, or a combination of the above. No hypothesis could be proven due to the high degree of underlying genetic similarity possessed by all the tested Balkan groups. The linguistic and cultural differences among various Balkan groups were thus deemed to be have not been strong enough to prevent significant gene flow among the above groups. Bosch et al. did, however, conclude that there was no significant external genetic input from Italy.
Many Vlachs were shepherds in the medieval times, driving their sheep through the mountains of Southeastern Europe. The Vlach shepherds reached as far as Southern Poland and Moravia in the North (by following the Carpathian range), Dinaric Alps in West, the Pindus mountains in South, and as far as the Caucasus Mountains in the east .
In many of these areas, the descendants of the Vlachs have lost their language, but their legacy still lives today in cultural influences: customs, folklore and the way of life of the mountain people, as well as in the place names of Romanian or Aromanian origin that are spread all across the region.
Another part of the Vlachs, especially those in the northern parts, in Romania and Moldova, were traditional farmers growing cereals. Linguists believe that the large vocabulary of Latin words related to agriculture shows that they have always been a farming Vlach population. Just like the language, the cultural links between the Northern Vlachs (Romanians) and Southern Vlachs (Aromanians) were broken by the 10th century, and since then, there were different cultural influences: