Subliminals, or subliminal messages, are signals or messages embedded in another medium, designed to pass below the normal limits of perception. These can be in the form of audio or visual cues that are not consciously noticed but may influence the subconscious or deeper mind. In marketing, subliminal messaging is a controversial technique, and its effectiveness and ethical implications have been subjects of debate. The idea is to influence behavior or decision-making subtly, but there's limited scientific evidence supporting its effectiveness in advertising.