Which term indicates that something is observable or able to be seen?

The term that indicates something is observable or able to be seen is "visible." This word specifically refers to the quality of being able to be perceived by the eye or observed in a way that is clear and apparent. Something that is visible stands out and can be easily recognized or detected without the need for special conditions or tools.

In contrast, words like "concealed," "transparent," and "hidden" refer to the opposite concept. "Concealed" and "hidden" imply that something is intentionally obscured or covered up, making it difficult or impossible to see. "Transparent," while it might suggest clarity, usually refers to the ability to see through something rather than something being readily observable itself. Thus, "visible" accurately captures the essence of being able to see or observe something directly.