The Citadel bailey (also referred to as the courtyard) is a section inside the Citadel.
The bailey is the training section for the initiates, each section with its own purpose. Here the initiates can practice with various weapons, improve Unarmed skills, and also learn how to wear powered armor, which is taught by Paladin Gunny.
Staying on the shooting range will make the initiates stop their training. When the Lone Wanderer moves from it, they will continue shooting.
The Citadel bailey appears only in Fallout 3.