What word captures the meaning of 'being hidden to wait for the right moment'?

The term that best encapsulates the idea of 'being hidden to wait for the right moment' is "lurk." This word conveys the sense of remaining in a concealed or less visible position, often with the intention of observing or waiting for an opportune moment to act. It implies a strategy of patience and stealth, suggesting a readiness to emerge at an appropriate time without drawing immediate attention.

In contrast, the other options present meanings that do not align with the concept of hiding or waiting stealthily. "Advertise," for instance, suggests actively promoting or making something known, which is the opposite of being hidden. "Expose" denotes revealing something that was previously concealed, directly contradicting the idea of remaining unnoticeable. Likewise, "reveal" implies the act of making something known or visible, which also does not relate to the notion of lurking in concealment. Therefore, "lurk" is the most fitting term for the meaning described in the question.