Opacity

noun

1. The state or quality of being opaque, not allowing light to pass through

   "We could not see the sandbar due to the opacity of the muddy water."

2. The state or quality of being inaccessible to understanding.

   "The opacity of these decisions is troubling."

3. A measure of relative impenetrability to electromagnetic radiation such as light.

   "The opacity of a clean glass window is near zero."