Notes on Defining of Computer-Mediated Communication, by John December
CMC Involves People
At the individual level, people use Internet tools to retrieve information, and communicate with others. Electronic mail is probably the most prevalent form of this kind of communication.
There's a wider range of activity in group communication on the Internet. Electronic mail, MU*'s, and other forms of text, audio, and video means exist.
To communicate at the mass level, it is often simply a matter of taking the tools from the group or individual level and applying them to larger numbers of people.
What differs is how people create relationships online. While non-CMC means of creating relationships require temporal and physical copresence, relationships online are can often be remarkably more fluid. You might make a passing acquaintance on a real-time text environment, have a conversation with them for a few minutes, and then never be in contact again.
Moreover, people involved in CMC perceive each other by mediation. This can lead to reduced social cues (Kiesler, 1986).