Meaning of officer of the guard

of'ficer of the guard'

Pronunciation: [key]
— Mil. Mil.
  1. an officer, acting under the officer of the day, who is responsible for the instruction, discipline, and performance of duty of the guard in a post, camp, or station. Abbr.: OG, O.G.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.