What does a fat finger mean?

"Fat finger" is a term that refers to input errors that are made when manually entering data into computers, via keyboards or touch screens. These errors occur especially in dynamic and stressful environments, such as stock exchanges and dealing rooms, and can sometimes have major financial consequences.

A fat finger error occurs when, for example, a trader accidentally enters an incorrect amount or quantity, resulting in huge orders being placed. This can lead to large price fluctuations, so-called "flash crashes," and chain reactions in financial markets, especially due to computer-controlled trading systems that react directly to price and volume deviations. It is a nightmare for every stock trader and has led to significant losses in the past.