What is subliminal perception? Give a famous example of when this was supposedly demonstrated.

Subliminal perception is the perception of stimuli below the level of consumer consciousness.
Examples may vary. For example:
In one well-known example, an experiment was performed at a New Jersey drive-in movie theatre in September 1957. During a showing of the movie Picnic, a firm called the Subliminal Projection Company inserted messages that said "Drink Coca-Cola" and "Eat Popcorn" for 1/3000 second every five seconds. This rate was too fast for viewers to be aware that they had seen the images. Supposedly, sales of popcorn increased by almost 20 percent and consumption of Coke by almost 60 percent. These claims created an uproar as journalists and social critics expressed fears that social scientists would team up with advertisers to invade privacy and control consumers against their will. As one magazine put it at the time, consumers' minds had been "broken and entered." This experiment was never replicated and the executive responsible for the test later admitted that he had made up the results.