JAZER, or JASER, in Ancient Geography, a Levitical city in the territory of the Amorrhites beyond Jordan, 10 miles to the west, or rather south-west, of Philadelphia, and 15 miles from Ezebon, and therefore situated between Philadelphia and Heshbon, on the east border of the tribe of Gad, supposed to be the Jazorem of Josephus. In Jeremiah xlviii. mention is made of the sea of Jazer, that is, a lake; taken either for an effusion or overflowing of the Arnon, a lake through which it passes, or from which it takes its rise.