"Communication" implies two different, and sometimes conflicting, things. On the one hand, it means to have a thoughtful exchange of views (dialogue) with a small number of people, perhaps just one. But it can also mean to disseminate broadly a simple message (compare broadcasting), without deep thought or appeals for feedback. The Latin root word comunicare means "to make common."
Communication as a field of study is relatively new. Arguably, it encompasses journalism, public relations, media studies (which might include the study of television, radio, and film), and rhetoric, among other fields.
We might divide these diverse fields into those which cultivate a thoughtful exchange between a small number of people (debate, talk radio, e-mail, personal letters) on the one hand; and those which disseminate broadly a simple message (public relations, television, Hollywood films.)
The view people take to communication is changing, as new technologies change the way people communicate and organize. This new trend in communication, decentralized personal networking, is termed smartmobing.