Definition - What does Hot Server mean?
A hot server is a standby machine that receives regular updates and is able to step in in the event of a failover. The hot server waits in backup operational mode, behaving as a standby server unti the main server fails.
As a type of backup server, a hot server can be an important component of an organization's disaster-recovery plan.
Techopedia explains Hot Server
There are also cold servers and warm servers. A cold server is a backup server that replaces a lost main server. It is turned on once so that software can be installed and configured, and then is turned off until a failover occurs. A warm server, often used for mirroring and replication, is a server that is turned on periodically to receive updates from the main server it is backing up. It is then shut down until it requires further updates or is needed to replace the main server.