The proteins and connective tissue of mammals (animal fat) which is somehow turned into some type of unnatural substance that one injects under their skin. It is mainly used by ragged, thin lipped hookers who have spent too much time sucking cock without sunscreen on their mouths or something (exp: Lisa Rinna, Jessica Simpson). It is also used to smooth out wrinkles and make you look like a zombie freak (exp: Nicole Kidman).
suzy: "What happened to Karen? She's hideous."
sharon: "She didn't like her thin lips so she got collagen injections."
suzy: "It looks like someone punched her in the mouth."