Maybe I'm missing something obvious, but I don't understand what that graph is trying to tell me. If the horizontal axis is x... what is the vertical axis? Wh

Maybe I'm missing something obvious, but I don't understand what that graph is trying to tell me. If the horizontal axis is x... what is the vertical axis? What does the shaded wedge represent? It certainly doesn't represent "x>1" in any way I'm familiar with. (A vertical line at x=1, with the space to the right shaded, I could see...)