What does 'opaque' mean?

The term 'opaque' primarily refers to a material that does not allow light to pass through, making it impenetrable. This definition extends beyond the physical properties of materials to describe concepts or ideas that are difficult to understand or interpret. When something is opaque in a metaphorical sense, it can imply a lack of clarity or an incomprehensible nature, which aligns perfectly with the understanding that such things are hard to grasp.

In this context, the other choices do not align with the definition of 'opaque.' The options that suggest transparency, readability, or shininess directly contradict the essence of what it means for something to be opaque, as they imply clarity and understanding rather than obscurity or impenetrability. Therefore, the choice identifying 'opaque' as impenetrable to light and hard to understand accurately captures the word's full meaning.