watermarkwa·ter·mark /ˈwɔːtəmɑːkˈwɒːtərmɑːrk, ˈwɑː-/ noun [countableC]1a design that is put into paper that you can see when you hold it up to the lightBanknotes have a watermark to prevent forgery.
2COMPUTING an electronic device in text, pictures, music etc in DIGITAL form, showing where they came from. Watermarks can be used to fight against illegal copyingA digital watermark through music bought over the Internet will show the original purchaser.