“Private” is one of eight post statuses available in WordPress. These statuses control whether WordPress posts are visible to the entire world, waiting for moderation, or sent to the trash to await deletion.
When you write in WordPress, you will most commonly see the Draft, Pending Review and Publish statuses.
The Private status is used less frequently, but it can be useful in some situations. Private posts are for content that you only want high-level users to see. These posts are most useful for internal communication and documentation. I would not recommend storing top-secret information in these posts, but rather want to hide content from regular users.