An anchor channel is the television station that you stay on while searching for something better to watch. The show that is on isn't your favorite show, but it's enough to hold you over until you find something better to watch.
"Man, I can't find anything good to watch."
"Just use ESPN as your anchor channel, bro."
The channel on which you stay while looking for a much better program; applicable to TV, radio, etc.
Guy 1: Dude, why are we watching MadTV?
Guy 2: Shut up, it's the anchor channel while I look for something better... Ooh, Bad Boys 2!
Guy 1: Hellz yeah.