File Extensions What Are File Extensions? SUMMARY: File extensions defined. This tip explains what the usually three characters are for.   In general terms, a file format in the PC world signifies what type of information is containing in a particular file. These are usually designated by the one to four (usually three) characters (the extensions) after the period in a filename. For example: Filename: readme.txt The "txt" designates the file format of this particular file, a plain-text file. Filename: game.exe The "exe" designates the file format of this particular file, an executable file. Note that file extensions do not always signify the type of information inside a file; sometimes programmers hide the type of content inside a file with fake extensions. Also, some filenames may have multiple file extensions that can trick you into opening a Trojan Horse. However, this is a Windows tweak that can help you find files with multiple extensions. More information about these and other particular file type can be found in this section's tips on MalekTips.   Add: Del.icio.us | Digg | Furl | My Yahoo!   Discuss This Tip Print This Tip Get E-Mail When New Tips are Online Return to the File Extensions page.