H. Lasswell's definition of communication is "who says what to whom by what means and to what effect."
The three functions of media are to entertain, inform, and persuade.
There are four types of communication: intra-personal (daydreams and internal monologues), interpersonal (discussion in small groups), group (discussion with large groups, such as public speaking), and mass (technology-driven communication with thousands or millions of people). The system of communication which brings news and entertainment to the populace at large through books, newspapers, radio, television, and the Internet is called the "Mass Media."
The Mass Media is playing an increasingly large role in our everyday lives. The term mass media is mainly used by academics and media-professionals. When members of the general public refer to "the media" they are usually referring to the mass media, or to the news media, which is a section of the mass media.
Mass media is a term used to denote, as a class, that section of the media specifically conceived and designed to reach a very large audience (typically at least as large as the whole population of a nation state). It was coined in the 1920s with the advent of nationwide radio networks and of mass-circulation newspapers and magazines. The mass-media audience has been viewed by some commentators as forming a mass society with special characteristics, notably atomization or lack of social connections, which render it especially susceptible to the influence of modern mass media techniques such as advertising and propaganda.
The mass media system has controls: media monitors whom ensure that bad messages are cut down or eliminated. These include regulators (such as the FCC), pressure groups (such as the Catholics, whose power is leveraged through boycotts), and gatekeepers, such as editors, directors, and corporate moguls like Rupert Murdoch. A classic example of a gatekeeper exercising control was when NBC fired Phil Donohue over ideological differences.
Another control is perceived public opinion. For example, the press doesn't like to run photos of the dead or injured from war, for fear of public outrage.