Some other group, like the mob or the public press, that had an unofficial but often great influence on public affairs, was called the fourth estate. In the 19th century, fourth estate came to refer exclusively to the press, and now it's applied to all branches of the news media. More @Wikipedia
Hover over any link to get a description of the article. Please note that search keywords are sometimes hidden within the full article and don't appear in the description or title.