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

APP file extension

Mac OS X Application

Executable Files

DBF file extension

Database File

Database Files

DLL file extension

Dynamic Link Library

System Files

DOCX file extension

Microsoft Word Open XML Document

Text Files

DTD file extension

Document Type Definition File

Developer Files

FLV file extension

Flash Video File

Video Files

GZ file extension

Gnu Zipped Archive

Compressed Files

MDB file extension

Microsoft Access Database

Database Files

MIM file extension

Multi-Purpose Internet Mail Message File

Encoded Files

TARGZ file extension

Compressed Tarball File

Compressed Files

TXT file extension

Plain Text File

Text Files

VOB file extension

DVD Video Object File

Video Files

XLR file extension

Works Spreadsheet

Spreadsheet Files

ZIPX file extension

Extended Zip File

Compressed Files

3DM file extension

Rhino 3D Model

3D Image Files