"publicity or press agent," 1945, also by that year as a verb, said to have been coined at show biz magazine "Variety" (but the first attested use is not in "Variety") and supposedly from name of Gene Flack, a movie agent, but influenced by flak. There was a Gene Flack who was an advertising executive in the U.S. during the 1940s, but he seems to have sold principally biscuits, not movies.
权威例句
1. Once the cold water enters the flack, the vapor pressure falls quickly.
一旦冷水进入长颈瓶, 水气压就迅速下降.
2. Test shows that testing system can accomplish all signal test of the flowing system for flack.
验证表明该测试平台能完成某型高炮随动系统所有信号测试.
3. A test device for flack flowing systems based on virtual instrument technology is developed.