Page Owner and Administrators
Pages can be locked to specific users, and groups.
In general, locked pages can only be accessed by the designated users, or the users belonging to the designated groups.
There are however 3 special cases to permissions that break away from that:
1) users in the Jira Administrators group always have read/write access to all pages.
This exist intentionally, to avoid the possibility of users locking themselves out of a page, or a page being rendered entirely inaccessible.
2) the owner of a page always has read/write access to a page.
This is to prevent accidentally locking out the owner. If necessary, you can change the owner of a page.
3) On Jira Server / Data Center, you can mark a page as publicly accessible.