Jerah is one of may sons of Joktan, one of two sons of Eber (Genesis 10:26). The Joktanites are the last mentioned Shemite generation before the tower of Babel is built. Joktan's brother Peleg eventually brings forth the family of Abraham.
The name Jerah is identical to the word (yerah) meaning month, and (yareah), moon. The month was the primary unit of time in the Semitic world.
Where this word for moon comes from is unknown. Some have suggested it comes from ('arah), wander or journey, as the moon is the most ambulant body in the sky. Another common designation for the moon reflects it whiteness: (lebana) from the untranslated root (lbn), where also the name Laban (White Guy) comes from.
NOBS Study Bible Name List and Jones' Dictionary of Old Testament Proper Names agree: the name Jerah means Moon.