Blotting paper is a type of paper or other material which is used in a desk blotter to absorb an excess of substance (such as ink or oil) from the surface of an object.
Examples of its use include absorbing the excess ink left on parchment after writing with a fountain pen, removal of excess lipstick or facial oils in cosmetic testing, or removal of excess dye after staining.
When used to remove ink from writings, the writing may appear in reverse on the surface of the blotting paper, a phenomenon which has been used as a plot device in a number of detective stories.
Blotter can also refer to an official summary, usually covering a short duration, such as a police blotter, or the trade confirmation summary of a financial institution. The term is frequently used in financial institution software terms to represent a list of current trades in a spreadsheet-like interface whose status is updated in real-time. The trades are often highlighted in different colours depending on their status.