Beth Nahrain or Bet Nahrain or (Syriac: ܒܝܬ ܢܗܪ̈ܝܢ; "house (of the) rivers") is the Assyrian name for the region known as Mesopotamia in the Syriac language (Greek "land between the rivers") as well as its surrounding periphery. Geographically, it refers to the areas around the Euphrates and Tigris rivers (as well as their tributaries). The Aramaic name loosely describes the area of the rivers, not between the rivers, as the literal Greek term does, but both names refer to the same region.
While it may be erroneously thought that the name is derived from the Greek "Mesopotamia", the opposite is more probable. The Aramaic name has been attested since the adoption of Old Aramaic as the lingua franca of the Neo Assyrian Empire in the 8th century BCE, but the Greek name Mesopotamia was first coined in the 2nd century BCE by the historian Polybius during the Seleucid period. The name Bayn al-Nahrayn is also found in Arabic (بين النهرين; "between the two rivers").
This area roughly encompasses almost all of present-day Iraq, parts of southeastern Turkey, and northeastern Syria. The Assyrians are considered to be indigenous inhabitants of Beth Nahrain. "Nahrainean" or "Nahrainian" is the Anglicized name for "Nahraya", which is the Aramaic equivalent of "Mesopotamian".