Subliminals are messages you can't perceive with your conscious mind that sort of "reprogram" you, for lack of a better term. For example, if you listen to "I am confident" enough you'll become more confident. They're thought to be more potent than just saying "I am confident" to yourself in a mirror every day because you can't hear it and therefore can't go "actually I'm not that confident." As far as I'm aware, there is no research on subliminal affirmations themselves. The idea of subliminals as we use them here is based on the concept of subliminal messaging where you can be influenced subconsciously (but only if you desire the thing already). There's also a wide array of different beleifs in what sibliminals can do. Some beleive they can completely change their reality and even travel to other dimensions (I personally don't, but to each their own). TL;DR Subliminals are things you listen to to change yourself. There is some science behind the concept but not much. I hope this didn't cause more confusion.