What is the best description of something that is intended to be kept secret?

The best description of something that is intended to be kept secret is "confidential." Confidentiality refers to the obligation to protect sensitive information from being disclosed to unauthorized individuals. This term is commonly used in legal, medical, and professional contexts, where certain information must be safeguarded to maintain privacy and trust. By labeling information as confidential, it signals that the details are only to be accessed or shared among those who have the appropriate clearance or need to know, thereby protecting against potential misuse or harm that could arise from unauthorized access.

In contrast, the other terms describe states where information is accessible or meant for public consumption. "Open" suggests a lack of restrictions on information access, "public" indicates that information is available to anyone, and "transparent" typically refers to the quality of being clear and open about actions and decisions, further emphasizing accessibility rather than secrecy. Thus, "confidential" accurately captures the essence of something meant to remain secret.