You never know when set notation is going to pop up. Usually, you'll see it when you learn about solving inequalities, because for some reason saying x < 3 isn't good enough, so instead they'll want you to phrase the answer as the solution set is { x | x is a real number and x < 3 }.
If the skin really looks like the color of ash, a deeper more persistent gray or gray-blue color, this could potentially be due to a side effect of certain medications, with or without interaction from sunlight.
Causes: It is caused by yeast called Malassezia, which normally exist in small numbers on the skin. Certain conditions however, can cause the overgrowth of the yeast, causing the development of white and reddish-brown spots on skin.