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

ACCDB file extension

Access 2007 Database File

Database Files

APP file extension

Mac OS X Application

Executable Files

CFG file extension

Configuration File

Settings Files

CSR file extension

Certificate Signing Request File

Web Files

DOC file extension

Microsoft Word Document

Text Files

H file extension

C/C++/Objective-C Header File

Developer Files

HQX file extension

BinHex 4.0 Encoded File

Encoded Files

ICNS file extension

Mac OS X Icon Resource File

System Files

LUA file extension

Lua Source File

Developer Files

MAX file extension

3ds Max Scene File

3D Image Files

PDB file extension

Program Database

Database Files

PDF file extension

Portable Document Format File

Layout Files

SQL file extension

Structured Query Language Data File

Database Files

TXT file extension

Plain Text File

Text Files

XCODEPROJ file extension

Xcode Project

Developer Files