File extensions
From The Glossary of Digital Photography
The three letters on the end of a file format that tell the computer, and the user, what type of file is being accessed. Some examples are .jpg, .tif, and .gif. See also file format

ONLINE GLOSSARY OF DIGITAL PHOTOGRAPY
The three letters on the end of a file format that tell the computer, and the user, what type of file is being accessed. Some examples are .jpg, .tif, and .gif. See also file format