noun

• (figuratively, informal) Adverse criticism.
  "There’s always been a built-in backlash against big-scale caprices like Raiders of the Lost Ark from people who think that $20 million should be spent on more than entertainment for its own sake. Raiders may also get flak for not being as cuddly-lovable as Star Wars, or for using those old reliables – the Nazis – as villains, or for dazzling the audience with an almost brazen self-confidence."
• (informal) A public-relations spokesperson.
  "2006, Edward Herman, Noam Chomsky, A Propaganda Model, in 2006 [2001], Meenakshi Gigi Durham, Douglas Kellner (editors), Media and Cultural Studies: Keyworks, revised edition, page 277, AIM head, Reed Irvine's diatribes are frequently published, and right-wing network flaks who regularly assail the “liberal media,” such as Michael Ledeen, are given Op-ed column space, sympathetic reviews, and a regular place on talk shows as experts."