This is an additional space inside tents, where you can store your stuff. They are usually located at the front or the sides. You can also change your wet and muddy gear in the vestibule area. You can also cook your dinner inside the vestibule in windy conditions. You also get add-on vestibules that you can attach to the front part of the tent. Side vestibules are also particularly useful. They can improve the livability factor of tents.