What is "yellow journalism"?
Yellow journalism is the kind of screaming, exploitive headline associated with the Hearst newspapers circa 1900.
The Hearst newspapers (prominently the San Francisco Daily Examiner and the New York Journal ) of the turn of the century enjoyed a somewhat reckless reputation. They are credited with egging on the Spanish-American War by insinuating that the USS Maine was blown up by Spanish saboteurs (It wasn't) and emboldening a shameless grab of Spanish colonial holdings in the 1890s.
Another feature of the Hearst newspapers was the first ongoing American comic strip, "The Yellow Kid." (In an unusual move, this panel strip ran in color, with the main character's ankle-length shirt colored yellow.) This is the origin of "yellow" journalism.
This style of journalism was known in the late 20th Century as "tabloid" journalism ("Tabloid" refers to newspapers that are half the page size of traditional broadsheet newspapers; these include supermarket papers like The National Enquirer and city newspapers like The New York Post ) and today is primarily associated with Fox News.