This entry incorporates text from the public domain Easton's Bible Dictionary, originally published in 1897.
Adullam is a region of Israel near the Valley of Elah (to the south of Bet Shemesh), west of Gush Etzion. The villages of Aderet, Neve Michael/Roglit, and Aviezer are located here. In the 1950's there were plans to set up Adullam as a formal political/economic region, on the model of Lachish, but the plans were not carried out. Plans from the 1960's called for a Moshav called Adullam to be established, contiguous with Moshav Aderet, but this plan too did not materialize, and the preliminary legal framework for Moshav Adullam was dismantled a few years ago.
Adullam was also one of the royal cities of the Canaanites (Joshua 12:15; 15:35) referred to in the Hebrew Bible. It stood near the highway which later became the Roman road in the Valley of Elah, the scene of David's memorable victory over Goliath (1 Sam. 17:2), and not far from Gath. It was one of the towns which Rehoboam fortified against Egypt (2 Chronicles 11:7). Micah calls it "the glory of Israel" (Micah 1:15).
I Samuel refers to the Cave of Adullam, and reports that David, when he had been expelled from the court of King Saul, there gathered together "every one that was in distress, and every one that was in debt, and every one that was discontented" (1 Sam. 22:2). According to tradition this cave was at Wadi Khureitun, between Bethlehem and the Dead Sea, but there is little evidence for this view. However, the site at 'Aid-el-ma, about 4 km south of the Valley of Elah, and about 20 miles west from Bethlehem, is now more commonly accepted. At this place is a hill some 140 m high pierced with numerous caverns, some of them large enough to hold 200 or 300 men.
An Adullamite can mean an inhabitant of Adullam, and the word is used in this sense in Genesis 38:1, 12, 20. However, by reference to the passage in 1 Samuel mentioned above, it has come to mean someone who is plotting against the established leadership of a political party or other group, a group of such plotters being called a Cave of Adullam. John Bright described a 19th century plot within the leadership of the United Kingdom Liberal Party, directed against the 1866 Reform Bill, in these terms (see Adullamites).