To mark paper with a watermark.
To mark a datafile with a digital watermark.
A mark indicating the level to which water has risen.
A translucent design impressed on the surface of paper and visible when the paper is held to the light.
A logo superimposed on a digital image, a television broadcast, etc.
A value stored in a datafile to ensure its integrity, so that if the file's contents are changed then the watermark will no longer match the contents.