To be 'opaque' means to be:

The term 'opaque' specifically refers to objects or materials that are not transparent, meaning that light does not pass through them. This quality makes them difficult or impossible to see through. In addition to its physical meaning, 'opaque' can also describe concepts that are hard to understand or not easily interpreted. For instance, a text or argument that lacks clarity can be described as opaque, as it obscures understanding rather than enhancing it. Therefore, the correct choice captures both the literal and figurative uses of the term effectively.