Privacy, secrecy, isolation, and sequestration all refer to keeping someone or something protected or hidden from others. Privacy and secrecy are particularly concerned with preventing others from knowing about one's actions, thoughts, and communications. In general, secrecy implies that people who are not directly involved in a matter are completely unaware of it; whereas privacy implies only that those who are not involved, though aware of the matter, are prevented from knowing the details. For example, a teenager might keep a private diary, which her parents know about but which is kept locked so that they cannot read it, or a secret diary, the very existence of which is kept hidden from her parents. Or the leaders of two countries might meet in private, meaning that the fact of the meeting might be widely known but only the leaders themselves know what they said to each other; but if they want to meet in secret, they take steps to prevent the general public from finding out that the meeting took place at all.
Isolation and sequestration generally signify physical separation. In contrast to privacy and secrecy, which are usually sought by the individuals involved, isolation and sequestration are often imposed by others. For example, a vulnerable medical patient might be kept in isolation to protect him from acquiring an infection through contact with others, or a prisoner might be placed in isolation—that is, in solitary confinement—as punishment for an infraction. Sequestration can refer to things as well as to people, and is most often used to specify separation in technical or legal contexts: Carbon sequestration in the coal industry can potentially alleviate the problem of global warming; Sequestration of the jury she was serving on kept her away from her family for weeks; Until its leaders comply with international agreements, sequestration of that nation's overseas bank accounts will remain in effect.
One wants to keep one's secrets secret, and as well, keep many aspects of one's life private. But the ability of powerful corporations, government intelligence agencies, online stores, social media, or even individual thieves to reach and probe into our personal communications, buying habits, financial resources, circle of friends, and general lifestyle poses threats to one's privacy. Fortunately, for most people, reasonable precautions are usually enough to allow them to engage in normal activities without great worry.