The first document in which the term "Ultra siluam" is used referring to the area dates from 1075, its meaning is "beyond the forest". The terms "Partes Transsylvanæ" ("parts beyond the forest") dates from the same century (in Legenda Sancti Gerhardi) and after that becomes the term used in the Latin documents of the Kingdom of Hungary (as "Transsilvania").

Transylvania

From Transilvania, the Latin name meaning "beyond the forest" ("trans" = beyond and "silva" = forest).

Ardeal/Erdély

The names of Ardeal in Romanian and Erdély in Hungarian are believed to be linked one to another. The original source and meaning are disputed and claimed by both Romanians and Hungarians. The first form ever recorded was "Erdeuelu" in the 12th century Chronicles of Anonymus (Gesta Hungarorum), while the first Romanian form recorded was in 1432 as "Ardeliu".

The initial a/e difference between the names can be found in other words common to Romanian and Hungarian, such as agriş / egres (gooseberry).

The ending '-eal' in Romanian suggests that it was not borrowed in Romanian from Hungarian, because as we know from parallel examples, Hungarian '-ely' becomes '-ei' in Romanian (Hungarian Udvarhely → Romanian Odorhei).

The actual meaning is yet unknown, there have been suggested several possible etymologies:

• arde appears to be an Indo-European word meaning "forest" (akin to Forest of Arden, England and Belgian Ardennes Woods). However, there is also a Hungarian word erdő, which also means "forest", but with a unknown etymology: it could be that it was borrowed from the Indo-European (Celtic or Dacian) or derived from the Finno-Ugric word "Ered" which means to orginate or to grow. The word for "forest" could be akin to the Latin name of Transylvania.
• deal means "hill" in Romanian, while arde means "to burn": it has been suggested that it could mean "the land of the burning hills" after the fires started by Romanian shepherds to warn the invaders of their presence.
• ered is a known Indo-European root that meant 'high, steep'. From this root is the Latin word Arduus, meaning 'steep, towering, difficult to reach'. 'Ardeal' may also be from this root, referring to the high elevation.
• Arderich , the king of the Germanic Gepids once ruled Transylvania in the 5th century and it is possible that the name of Arderich's land was passed on ever since.

Siebenbürgen

Siebenbürgen, the German name for Transylvania, first appeared in a document dated 1296. Translated from German, Siebenbürgen means "seven cities" or "seven boroughs", after the seven German cities founded or settled by the German Saxons in Transylvania: Klausenburg (Cluj), Kronstadt (Braşov), Hermannstadt (Sibiu), Schässburg (Sighişoara), Mediasch (Mediaş), Mühlbach (Sebeş), and Bistritz (Bistriţa). An alternate Latin version, "Septem Castra" ("Seven fortresses") was also used in Mediaeval documents.