Earned media refers to favorable publicity gained through promotional efforts other than advertising, as opposed to paid media, which refers to publicity gained directly through advertising.
Earned media often refers specifically to publicity gained through editorial influence, whereas social media refers to publicity gained through grassroots action, particularly on the Internet. According to Wikipedia sources, the media may include any mass media outlets, such as newspaper, television, radio, and the Internet, and may include a variety of formats, such as news articles or shows, letters to the editor, editorials, and polls on television and the Internet.
Most importantly, earned media cannot be bought or owned, it can only be gained organically, hence the term "earned." As such, it lifts the impact of paid and owned media.