well, a host is a computer connected to a network. Like in LAN, you can call the connected PCs as hosts. Although you can use words like computer-1 etc but host is a standard word and has the same meaning.
No, a host may not me in a domain.
Just like you say node in graphs, the same way you say host in networking.
The system that contains the data is called the host, while the computer at which the user sits is called the remote terminal. A computer that is connected to a TCP/IP network, including the Internet. Each host has a unique IP address.
"Hosts" may refer to the hosts file, a file that serves to look up Internet Protocol addresses.