The fairness doctrine was a legal rule that required broadcasting companies to cover issues of public importance and to do so in a way that was fair and took different points of view on issues into account. The doctrine is no longer in force. It was rescinded in the 1980s.
The fairness doctrine had its origins in the 1940s. The government decided that it had the right to regulate what was broadcast and, beyond that, that it had the right to actually tell broadcasters to air certain things (as opposed to just saying what they could not broadcast). The idea was that the broadcasters were using public airwaves to get their messages across and they therefore could be regulated.
In the 1980s, this doctrine was done away with. This was largely because the Reagan administration was opposed to government regulation in general. It was also partly because the government decided that the proliferation of cable channels meant that issues would be covered from a variety of points of view even without the doctrine. Therefore, the fairness doctrine no longer exists and television channels are free to present views that are completely biased.