Internet
The Internet is a large "network of networks." There is no
one network known as The Internet; rather, regional nets like SuraNet,
PrepNet, NearNet, et al., are all inter-connected
(nay, "inter-networked") together into one great living thing,
communicating at amazing speeds with the TCP/IP protocol. All
activity takes place in "real-time."
UUCP
The UUCP network is a loose association of systems all communicating
with the UUCP protocol. (UUCP stands for `Unix-to-Unix Copy
Program'.) It's based on two systems connecting to each other at
specified intervals, called polling, and executing any work
scheduled for either of them. Historically most UUCP was done with
Unix equipment, although the software's since been implemented on
other platforms (e.g. VMS). For example, the system oregano
polls the system basil once every two hours. If there's any
mail waiting for oregano, basil will send it at that time;
likewise, oregano will at that time send any jobs waiting for
basil.
BITNET
BITNET (the "Because It's Time Network") is comprised of systems
connected by point-to-point links, all running the NJE protocol.
It's continued to grow, but has found itself suffering at the hands of
the falling costs of Internet connections. Also, a number of mail
gateways are in place to reach users on other networks.