Messages that are too low decibel, or encoded in some way that bypass conscious filters and are deciphered by the subconscious. It is a highly controversial subject, subliminal reception is proven, whether or not it has any effect is debatable. They are said to be useful for dreams because dreams are made from substance, not command.
Subliminal
advertising enjoyed a long run in the early half of the 20th century, but were banned by the government from commercials. There is conflicting evidence as to whether or not it had any actual affect.
Related Links:
Subliminal Messages Tutorial
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