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

TEX file extension

LaTeX Source Document

Text Files

AZW file extension

Amazon Kindle eBook File

eBook Files

ACCDB file extension

Access 2007 Database File

Database Files

CPL file extension

Windows Control Panel Item

System Files

CFM file extension

ColdFusion Markup File

Web Files

DDS file extension

DirectDraw Surface

Raster Image Files

OBJ file extension

Wavefront 3D Object File

3D Image Files

PPS file extension

PowerPoint Slide Show

Data Files

KEYCHAIN file extension

Mac OS X Keychain File

Data Files

DMG file extension

Mac OS X Disk Image

Disk Image Files

XLSX file extension

Microsoft Excel Open XML Spreadsheet

Spreadsheet Files

7Z file extension

7-Zip Compressed File

Compressed Files

CGI file extension

Common Gateway Interface Script

Executable Files

HQX file extension

BinHex 4.0 Encoded File

Encoded Files

TXT file extension

Plain Text File

Text Files