A specification for a manner of communication. IP carries individual packets of data from one host to another. TCP makes use of IP and governs the flow of data packets. TCP also provides error checking and correction. In general, a single computer system with its own unique name and address.
Hosts can be single user or multiuser.
A host requesting a service. A host can be both a client and a server at the same time. Any task carried out by a server on behalf of a client. Distribution of computer resources is key. Computers are large and expensive.