A star note is a bank note that has an asterisk (*), or star, after the serial number

Serial number

A serial number is a unique number assigned for identification which varies from its successor or predecessor by a fixed discrete integer value...

. These have been used by various countries around the world including Australia

Australia

Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

 and United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

. In the US, The Bureau of Engraving and Printing

Bureau of Engraving and Printing

The Bureau of Engraving and Printing is a government agency within the United States Department of the Treasury that designs and produces a variety of security products for the United States government, most notable of which is paper currency for the Federal Reserve. The Federal Reserve itself is...

inspects currency for printing errors prior to releasing notes into general circulation. When notes are discovered that have been printed incorrectly (such as having the serial numbers upside down, etc.) the misprinted "error notes" are replaced with star notes because no two bills within a certain series can be produced with the same serial number. They are used to maintain a correct count of notes in a serial number run. By their nature, star notes are more scarce than notes with standard serial numbers and as such are widely collected by hobbyists. Some of the highest prices paid for modern (post-1928) U.S. banknotes have been for star notes.

A star note was also substituted for the last note in a block rather than printing a note with a serial number consisting of eight zeros. This practice is no longer in use, as the highest range of serial numbers is now reserved for uncut sheets sold to collectors, so regular notes intended for circulation do not reach the final serial number in the block.