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

BAK file extension

Backup File

Backup Files

DTD file extension

Document Type Definition File

Developer Files

EPUB file extension

Open eBook File

eBook Files

FNT file extension

Windows Font File

Font Files

GZ file extension

Gnu Zipped Archive

Compressed Files

OTF file extension

OpenType Font

Font Files

PHP file extension

PHP Source Code File

Web Files

PNG file extension

Portable Network Graphic

Raster Image Files

SQL file extension

Structured Query Language Data File

Database Files

SRT file extension

SubRip Subtitle File

Video Files

SYS file extension

Windows System File

System Files

VCD file extension

Virtual CD

Disk Image Files

XCODEPROJ file extension

Xcode Project

Developer Files

XLR file extension

Works Spreadsheet

Spreadsheet Files