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

XCODEPROJ file extension

Xcode Project

Developer Files

CFG file extension

Configuration File

Settings Files

7Z file extension

7-Zip Compressed File

Compressed Files

JAR file extension

Java Archive File

Executable Files

XLSX file extension

Microsoft Excel Open XML Spreadsheet

Spreadsheet Files

DLL file extension

Dynamic Link Library

System Files

BAT file extension

DOS Batch File

Executable Files

RA file extension

Real Audio File

Audio Files

DB file extension

Database File

Database Files

M3U file extension

Media Playlist File

Audio Files

CAB file extension

Windows Cabinet File

System Files

VCD file extension

Virtual CD

Disk Image Files

KEYCHAIN file extension

Mac OS X Keychain File

Data Files

AVI file extension

Audio Video Interleave File

Video Files

DMG file extension

Mac OS X Disk Image

Disk Image Files