Idumea or Edom in Hebrew was the region south of Judea originally inhabited by the reputed descendents of Jacob's brother Esau.

Edom was periodically subjected to Judea (under David & Solomon [10th c. BCE] & the Maccabees [2nd c. BCE]). Homeland of the house of Herod. There were no natural boundaries between Idumea & Judea, so the borders were always in flux. The distinction between Edomites & Jews was blurred by Johanan Hyrcanus' forced conversion of Idumea to Judaism [ca. 130 BCE]. During the 1st c. CE pressure by the Arab Nabateans pushed the territory of the Edomites to within 15 miles of Jerusalem. The region was bounded by the city state of Gaza on the west and the Dead Sea on the east. Herod's wilderness fortress of Masada that served as the final base of Jewish resistance to Roman rule lay within its borders. After 70 CE Idumea was detached from Judea until it was captured by modern Israel in the Six-Day War [1967].

Sources: Into His Own

Ancient Jewish Cities & Regions: Idumea/Edom