The subliminal is below the liminal (the smallest detectable sensation).
Anything truly below the level of detectable sensation could not, by definition, be perceived. However, the subliminal is generally said to be below the threshold of conscious perception.
There is a widespread belief, not strongly supported by empirical research, that without being aware of its presence or content, a person’s behavior can be significantly affected by subliminal messages.
Thus, it is believed that one can influence behavior by surreptitiously appealing to the subconscious mind with words and images.
The fact that there is almost no empirical support for the usefulness of subliminal messaging has not prevented numerous industries from producing and marketing tapes which allegedly communicate directly with the unconscious mind, encouraging the “listener” not to steal, or coaching the “listener” to have courage or believe in his or her power to accomplish great things.