Evenness is the characteristic of being regular, smooth, or homogeneous. Part of what's beautiful about snow when it first falls is its undisturbed evenness.
When you're sanding the top of a table or spreading asphalt on a driveway, evenness is what you're aiming for. Another kind of evenness is a balance or equity between things: "The evenness of their salaries seemed fair to the restaurant's employees." Yet another way to have evenness is to be an even number, divisible by two — consider, for example, the evenness of the number 14 as opposed to the number 17.