Prana is used to refer to the breath. When we take a physical breath, there is a corresponding movement of prana in the subtle or astral spine. Prana flows up in the subtle spine in conjunction with the inhalation, and down with the exhalation.
This link between breath and the flow of prana is central to many of the techniques of meditation. By controlling the breath, which is easily felt, we can influence the flow of prana, which is much more subtle and difficult to feel.