Hi,
When the setting “New idea approval” is enabled, any idea that is posted does not get published automatically. It is added in the moderation queue, and the moderator can chose to approve or reject it. If approved, it is published to the ideaboard. If rejected, it can only be seen on the back end by the moderators and admin of the community.
Also, the status of any idea, even if directly published, can be changed to “Rejected”. This will hide it from the members, but it would be visible to the admins and moderators in the system.