A judge (士師) refers to a political and religious leader who appeared during the transitional period when the Israelite people moved from the patriarchal era to the monarchical era. They are also called Shoftim (判官).
These individuals normally engaged in daily life, such as farming or herding, but became leaders who guided the nation when major emergencies, such as war, occurred.
The biblical book that records their activities is Judges, and the history of this period was characterized by a cycle of the Israelite people's corruption - foreign invasion as God's discipline - the nation's repentance - the appearance of a judge - victory in war - and then corruption again.