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

SQL file extension

Structured Query Language Data File

Database Files

WMA file extension

Windows Media Audio File

Audio Files

EPUB file extension

Open eBook File

eBook Files

PS file extension

PostScript File

Vector Image Files

SDF file extension

Standard Data File

Data Files

EXE file extension

Windows Executable File

Executable Files

7Z file extension

7-Zip Compressed File

Compressed Files

PDF file extension

Portable Document Format File

Layout Files

CS file extension

Visual C# Source Code File

Developer Files

ACCDB file extension

Access 2007 Database File

Database Files

CSR file extension

Certificate Signing Request File

Web Files

MP4 file extension

MPEG-4 Video File

Video Files

KEY file extension

Keynote Presentation

Data Files

MSG file extension

Outlook Mail Message

Text Files

DMG file extension

Mac OS X Disk Image

Disk Image Files