Saugus.net: Glossary of Computer File Extensions

Filename Extensions List

So you see a file somewhere on the 'net with a name like "greatfile.xyz" and you would like to download it and use it on your computer. Will it work? What does the file extension xyz mean, anyway? This handy guide attempts to provide answers to those questions.

It is not meant to be read straight through; rather, it is meant to be a reference. An extension may be looked up either with the "find in page" option of your browser or by appending a "#xyz" (without the quotes and with xyz replaced by the extension in question) to the "go to" or "URL" field on your browser. There is also a Search Interface that will return not only the specific extension sought but also other entries that reference it. Be aware though that it assumes familiarity with the computer basics discussed on the terms page.

You may notice that most extensions are three letters (or fewer) long. This is due to a historical limitation of the operating system called CP/M (that was later inherited by MS-DOS). In fact, the whole concept of file extensions comes from CP/M. Most modern operating systems do not attribute any special meaning to the "." (period, or dot) character.

Be aware though that there is no standardization to filename extension usage, and many different people have used extensions to apply to many different things. This list only attempts to provide likely guesses of what something is apt to be. Programs that can make use of many of these extensions can be found on the Guide to Free Software.

If you want something added or see a problem with something already here (but keep in mind this guide is not meant to be overly technical) please send .

o & obj: A relocatable object file is the result of compiling a source file in any of several programming languages. It will be binary and will not be portable, and will not be runnable until it has been linked.
odb: An OpenDocument database file is the database format portion of the OASIS OpenDocument standard. It is usable by many different database applications.
odc: An OpenDocument chart file is a format used for storing chart data and is part of the OASIS OpenDocument standard. It is usable by many different applications.
odf: An OpenDocument formula file is a format used for storing mathematical data and is part of the OASIS OpenDocument standard. It is usable by many different applications.
odg & otg: An OpenDocument graphics file is the drawing format portion of the OASIS OpenDocument standard. It is usable by many different drawing applications. The version with the "d" is an ordinary document; the version with the "t" is a template for building other documents.
odi: An OpenDocument image file is a format used for storing image data and is part of the OASIS OpenDocument standard. It is usable by many different applications.
odp & otp: An OpenDocument presentation file is the presentation format portion of the OASIS OpenDocument standard. It is usable by many different presentation applications. The version with the "d" is an ordinary document; the version with the "t" is a template for building other documents.
ods & ots: An OpenDocument spreadsheet file is the spreadsheet format portion of the OASIS OpenDocument standard. It is usable by many different spreadsheet applications. The version with the "d" is an ordinary document; the version with the "t" is a template for building other documents.
odt & ott: An OpenDocument text file is the word-processing format portion of the OASIS OpenDocument standard. It is usable by many different word-processing applications. The version with the "d" is an ordinary document; the version with the "t" is a template for building other documents.
oga & ogg: The Ogg Vorbis format is an advanced binary audio format similar to (but more capable than) the mp3 format. It is patent and royalty free, and is supported on most platforms.
ogv: The Ogg Theora format is an advanced binary video format that is patent and royalty free, and is supported on most platforms.
opf: An open e-book package will use this extension. It is binary, but applications to read it exist or are being developed for a number of different platforms.