Blotter is a term used for official summaries of events and other details that have been recorded over a short period of time. In the world of finance, blotter refers to a book used by brokerage firms to account for the various trades it is involved in. Such information is recorded over a certain period of time. This often comes in the form of a computer software program set up for the purpose of recording transactions for financial entities; data is then recorded with the help of an information feed.

A blotter can provide information on the different aspects of trade. Examples of these are whether the trade involved a sale or a purchase of shares, the value of the shares involved, information on whether or not a trade was cleared, as well as the time and date of each transaction. Such information is recorded methodically, and may be marked or color-coded depending on the status of each entry.

Blotters are created for the purpose of recording pertinent trading information that may have to be reviewed by the brokerage firm. If any information needs to be confirmed, traders can refer to the trade blotter. Blotters may differ depending on the needs of the firm and can be very useful in the both the stock and bond market, as well as in the foreign exchange market. A blotter may also be referred to as an open book.