What does a fat finger mean?

"Fat finger" (also known as a 'dikkevingerfout' in Dutch) is a term that refers to input errors made during the manual entry of data into computers, via keyboards or touchscreens. These errors mainly occur in dynamic and stressful environments, such as trading floors and dealing rooms, and can sometimes have major financial consequences.

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