.localdomain was (yes *was*) a private domain for The Microsoft Network, just like .onion domain for the TOR network.
localhost is the name of the PC/tablet/phone/whetever you are currently working at. If you are using it as a TLD for your whole LAN or private network, please unplug your machine and let the Interenet recover.
.local is the network TLD for private use.
Biting the hand that feeds IT
