Wikipedia describes subliminal messages as "a signal or message embedded in another object, designed to pass below the normal limits of perception. These messages are indiscernible by the conscious mind, but allegedly affect the subconscious or deeper mind".
The term subliminal messages apply to many things.
The most common form is when a message flashes very quickly during an ad, movie or tv show.
The first time this kind was used was in 1957 by a market researcher James Vicary who had messages flashing every 1/3000 of a second with 5 second intervals saying “Drink Coca-Cola" and "Hungry? Eat popcorn" on a movie screen, in Fort Lee, New Jersey. Over the next month the theatres popcorn sales went up 18.1% and coke up by 57.8%.
James Vicary used this again in a Canadian broadcast saying phone in but after no increase of phone calls he admitted it to be a publicity scam
The next most common form is an optical illusion
These are seen every day and are very common but not usually thought of.Take this for example: show image of the two colour square things.
Another kind is used in music
Some musicians have backward messages in their music. These messages cant be heard by your conscious mind but your subconscious mind hears them. Queen used this in there song another one bites the dust where “Smoke marijuana, it's fun” can be heard backwards. Brittney Spears also has “Sleep with me I'm not to young” in hit me baby one more time but the most famous is in stairway to heaven by led zeppelin
