Rumelia (Rum İli, ; Rumeli; Ρωμυλία) was the name of a historical region in Southeastern Europe that was administered by the Ottoman Empire, corresponding to the Balkans. In its wider sense, it was used to refer to all Ottoman possessions and vassals in Europe that would later be geopolitically classified as "the Balkans". During the period of its existence, it was more often known in English as Turkey in Europe.
Rûm in this context means "Roman", and ėli means "land" and Rumelia (روم ايلى, Rūm-ėli; Turkish: Rumeli) means "Land of the Romans" in Ottoman Turkish. It refers to the lands conquered by the Ottoman Empire in the Balkans, which formerly belonged to the Byzantine Empire, known by its contemporaries as the Roman Empire. Although the term Byzantine Empire is used by modern historians, the empire's citizens and emperors called themselves Romans, meaning Christians, more specifically Greek Christians, and embraced a Christian identity. Various languages in the Balkans have long used the descriptor "Roman" to refer to the lands of the former Byzantine Empire. Indeed, today the term survives in the region as Rumelia; Rumelija; Румелия, Rumeliya; Ρωμυλία, Romylía, or Ρούμελη, Roúmeli; Macedonian; and Румелија, Rumelija. The old Latin documents in Genoa use the term Romania, the common name for the Byzantine Empire during the Middle Ages.
Originally, the Seljuks used the name "Land of the Rûm" (Romans) to define Anatolia, which the armies of the Seljuk Empire gradually conquered from the Byzantine Empire after the Battle of Manzikert in 1071. The Anatolian Seljuk Sultanate was called the Sultanate of Rum by its contemporaries, meaning the "Sultanate of the Roman Empire" or "Roman Sultanate", which mostly covered central Anatolia until the Battle of Köse Dağ in 1243. Anatolia was referred to as Land of the Christians, hence Rum. Afterwards, it was replaced by the Anatolian beyliks, among which the Ottoman Beylik rose to prominence in the 14th and 15th centuries and eventually became the Ottoman Empire.