Ghost banning is a process through which a user is invisibly banned from a social network, website or online community. Ghost banning enables an administrator to ban a user while still providing that user with the ability to browse through and use the available features, while still preventing the user from interfering with other users.
Techopedia explains Ghost Banning
Ghost banning first emerged in large social networks. It was implemented to identify, monitor and eliminate spammers and restrict their activities. For example, a ghost banned user can access the social network, review updates from his or her connections, etc., but none of that user's activity, such as content or link sharing, is visible to connections or even general subscribers. This enables the website administrator to segregate spammers from the lot and to put suspicious users under scrutiny until their activities are on par with the terms and conditions of the site in question.