The oxygen hemoglobin dissociation curve is a graph that describes the ability of hemoglobin to actually bind to oxygen at specific partial pressure values. Now, it turns out that the ability of hemoglobin to bind to oxygen is affected by several important factors. And one of these factors is the PH of our blood. So we when the PH of our blood changes, the hemoglobin's ability to bind to oxygen also changes. And this ultimately changes the oxygen hemoglobin dissociation curve. And this effect, as we'll see in just a moment, is known as the Bohr effect, which was named after the scientist who essentially described it, Christian Bohr.