File extensions – definition and basic information


File extensions are the integral parts of the files that are on each computer. Often, when working on a computer, we encounter a wide range of files, such as docx, ppt, part, mp3 or rmvb. We realize that they are there – but we often do not know what they are for on our computer.

File extension, also known as the filename extension is a suffix added to the name of a computer file, usually consisting of a number of characters placed after the last dot in the filename, which gives us information about its coding. In other words a file extension is a file format. It allows the operating system (e.g. Windows) to recognize what program it should try to open the file.

In the table below you will find a random selection of popular file extensions.


File extension The full name of the file Category

CFG file extension

Configuration File

Settings Files

COM file extension

DOS Command File

Executable Files

CUR file extension

Windows Cursor

System Files

DOC# file extension

Microsoft Word Document

Text Files

DTD file extension

Document Type Definition File

Developer Files

FLV file extension

Flash Video File

Video Files

ICS file extension

iCalendar File

Misc Files

KEYCHAIN file extension

Mac OS X Keychain File

Data Files

KML file extension

Keyhole Markup Language File

GIS Files

LNK file extension

Windows File Shortcut

System Files

LOG file extension

Log File

Text Files

M file extension

Objective-C Implementation File

Developer Files

MPG file extension

MPEG Video File

Video Files

RPM file extension

Red Hat Package Manager File

Compressed Files

XLR file extension

Works Spreadsheet

Spreadsheet Files