In DOS and some other operating systems, one or several letters at the end of a filename. Filename extensions usually follow a period (dot) and indicate the type of information stored in the file. For example, in the filename LETTER.DOC, the extension is .DOC, which indicates that the file is a word processing file. [1] [2] [3]

[1] Fios, E-Discovery Glossary, http://discoveryresources.org/01_electronic_discovery_glossary.html
[2] Vinson & Elkins LLP Practice Support, EDD Glossary.
[3] RSI, Glossary.

Attributions
- EDRM (http://edrm.net)