Ghosting

Ghosting is a technique used by the admin of a server where, instead of being in-world, they watch the console window of the server software which supplies chat logs and allows them to speak through the console to the users in-world. This allows moderation of a server without having to use the Minecraft client to monitor the world and therefore waste resources.

Method
To speak into the room, the admin uses the /say command on the console window. Their message appears in the room as though an op had used the command; it is yellow text with no player name. These omnipresent messages may cause player confusion but can be effective in defusing hostile situations such as arguments, verbal abuse and threats of griefing.

Terminology
The name comes from the fact that the admin has no physical manifestation in the room, and is a disembodied voice.