A file extension is a short series of letters and/or numbers at the end of a file name, used to indicate the type of file and the software that will run it. File extensions are usually 2-4 characters in length and use a period (.) to separate the file name from the extension.
| Extension | File Type | Program(s) That Open/Run File |
|---|---|---|
| .avi | Audio/Video Interleaved | Windows Media Player, WinAmp, QuickTime |
| .css | Cascading StyleSheet | Web Browser + HTML Webpage |
| .doc | Microsoft Word Document | Microsoft Word |
| .docx | Microsoft Word Document | Microsoft Word |
| .exe | Executable File | Usually An Install File |
| .flv | Flash Video File | FLV Player |
| .gif | Graphics Interchange Format | Image Editors/Viewers, Web Browsers, Etc. |
| .html | HyperText Markup Language File | Web Browser |
| .htm | HyperText Markup Language File | Web Browser |
| .jpg | Joint Photographic Experts Group File | Image Editors/Viewers, Web Browsers, Etc. |
| .jpeg | Joint Photographic Experts Group File | Image Editors/Viewers, Web Browsers, Etc. |
| .midi | Musical Instrument Digital Interface | Windows Media Player |
| .mid | Musical Instrument Digital Interface | Windows Media Player |
| .mp3 | MPEG Layer 3 Sound File | Windows Media Player |
| .mp4 | Streaming Media Video File | Windows Media Player |
| .mpeg | Motion Picture Experts Group File | Windows Media Player, Winamp, Etc. |
| .mpg | Motion Picture Experts Group File | Windows Media Player, Winamp, Etc. |
| .mov | QuickTime Movie | QuickTime |
| .qt | QuickTime Movie | QuickTime |
| Portable Document Format | Adobe Reader | |
| .png | Portable Network Graphics | Image Editors/Viewers, Web Browsers, Etc. |
| .rar | RAR Archive | 7Zip |
| .txt | Text File | Notepad, Wordpad, Vi, Etc. |
| .wav | Wave Sound File | Windows Media Player |
| .zip | Zipped File | Winzip |