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

APK file extension

Android Package File

Executable Files

BAT file extension

DOS Batch File

Executable Files

CSS file extension

Cascading Style Sheet

Web Files

DAT file extension

Data File

Data Files

DLL file extension

Dynamic Link Library

System Files

EXE file extension

Windows Executable File

Executable Files

IBOOKS file extension

Multi-Touch iBook

Data Files

ISO file extension

Disc Image File

Disk Image Files

JAVA file extension

Java Source Code File

Developer Files

MOV file extension

Apple QuickTime Movie

Video Files

MPG file extension

MPEG Video File

Video Files

PDF file extension

Portable Document Format File

Layout Files

RTF file extension

Rich Text Format File

Text Files

TARGZ file extension

Compressed Tarball File

Compressed Files

TXT file extension

Plain Text File

Text Files