The Y axis is the volume of air that is exchanged by the lungs given to us in milliliters. And the x axis is our time. Now notice as time increases, as time progresses, we have this fluctuating blue curve. And what the fluctuating blue curve essentially describes is it describes the process of breathing. Every time the blue curve increases, we essentially allow air into our lungs. And every time the blue curve decreases, we expel air from our lungs.