"Flak" (meaning an anti-aircraft gun or shrapnel therefrom) can also be spelled "flack." The phrase "taking flack" is either a literal or metaphorical use of th

"Flak" (meaning an anti-aircraft gun or shrapnel therefrom) can also be spelled "flack." The phrase "taking flack" is either a literal or metaphorical use of this meaning. A flack (never spelled without a c) is a public relations or press agent, and to flack is to promote something (or otherwise do the work of a flack).