What is the primary characteristic of something that is "transparent"?

The primary characteristic of something that is described as "transparent" is that it is visible through. This means that when looking at a transparent object, light can pass through it, allowing objects behind it to be seen clearly. Materials like clear glass or certain plastics are typical examples of transparency, as they do not obscure the view of what is on the other side.

The other characteristics mentioned do not align with the definition of transparency. Being heavy and dense suggests substantial physical properties that would inhibit visibility. Something that is hard to see through is the opposite of transparent, as it indicates opacity rather than clarity. Lastly, while a transparent surface may have reflective qualities, being possibly reflective does not meet the core definition of what it means to be transparent. Thus, the correct choice effectively captures the essence of transparency.