Concise Bible Dictionary:
A spring that formed the boundary of Judah and Benjamin (Josh. 15:9; Josh. 18:15). Identified by some with Ain Atan, 31° 41' N, 35° 10' E.
Potts’ Bible Proper Names:
Opening; opened, i. e., a spring:―boundary-line between Judah and Benjamin, Josh. 15:9. {Apertio}