A more thorough explanation:

A military judge is a public official appointed or elected to hear and decide legal matters in a military court. They are commissioned officers of the armed forces who are on active duty and are members of a bar of a federal court or of the highest court of a state. The Judge Advocate General of the particular service must certify a military judge as qualified for duty. A military judge of a general court-martial must also be a member of an independent judiciary. A military judge is detailed to every general court-martial and usually to a special court-martial.

For example, a military judge may preside over a court-martial proceeding for a service member who has been accused of violating military law. The military judge will hear evidence, make rulings on legal issues, and ultimately decide the outcome of the case.