Heater – term used to describe a piece of network equipment that is powered up, but does nothing or has no purpose.
Now that electricity actually costs real money, people are actually finding the heaters and removing them from the network, especially those old servers. It wasn’t so long ago that it wasn’t worth bothering to shut them off as the cost of labour exceeded the cost of leaving them running. This lead to tons the “crop rotation” model of data centres where you moved to a new data centre rather than fix the existing one.
Funny how things come around isn’t it.