Electronically stored information (ESI) is data and information that is created, manipulated, stored, transmitted, and utilized in digital form. Computer hardware, software, and networks are needed to utilize ESI. ESI, when used in conjunction with the Federal Rules of Civil Procedure (FRCP), is defined in detail in "Electronically Stored Information: The December 2006 Amendments to the Federal Rules of Civil Procedure," Kenneth J. Withers, Northwestern Journal of Technology and Intellectual Property, Vol.4 (2), 171. In 2006 the U.S. Government determined that it was necessary to legally define the phrase “electronically stored information,” and to describe the methods for maintenance and discovery when dealing with ESI.
For more information see "E-Discovery Q & A for Data Warehouse Administrators."