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

ASX file extension

Microsoft ASF Redirector File

Video Files

BAK file extension

Backup File

Backup Files

CS file extension

Visual C# Source Code File

Developer Files

FLA file extension

Adobe Flash Animation

Developer Files

HQX file extension

BinHex 4.0 Encoded File

Encoded Files

JAVA file extension

Java Source Code File

Developer Files

LOG file extension

Log File

Text Files

MSG file extension

Outlook Mail Message

Text Files

OTF file extension

OpenType Font

Font Files

PDF file extension

Portable Document Format File

Layout Files

PPTX file extension

PowerPoint Open XML Presentation

Data Files

VCXPROJ file extension

Visual C++ Project

Developer Files

XHTML file extension

Extensible Hypertext Markup Language File

Web Files

XLR file extension

Works Spreadsheet

Spreadsheet Files

3DS file extension

3D Studio Scene

3D Image Files