The idea that an advertising message presented to someone at a subliminal level will move them to action. Although the concept was popularized in books such as Vance Packard's The Hidden Persuaders (1957), the success of of such advertising is debatable.
The idea that subliminal advertising works was attributed to James Vicary (who coined the expression). Supposedly, he placed messages such as "Hungry? Eat Popcorn" for 1/3000 of a second at various times throughout a showing of the movie Picnic. Sales for popcorn supposedly went up almost 58%. Because of this, in 1974, the FCC banned subliminal advertising from radio and television.
Vicary eventually confessed that he had falsified the data from his experiments and some critics doubt that he had performed the tests at all. To this date, there is no evidence that such advertising works, but many people strongly believe in its efficacy.