True, "mainstream media" (rather than just mainstream) is quite often a word used by conspiracy theorists for the last 60 years or so.
Disagree with the second part, obviously. The media cover up a lot of things. A natural consequence of their tight relations to secret services like CIA and MI6.
Not going to discuss conspiracy theories today, but this... is just factually incorrect. Its been widely in use for more than a hundred years and in a wide array of subjects, most with no connection to conspiracy theories.