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

7Z file extension

7-Zip Compressed File

Compressed Files

LOG file extension

Log File

Text Files

VCF file extension

vCard File

Data Files

AVI file extension

Audio Video Interleave File

Video Files

SQL file extension

Structured Query Language Data File

Database Files

CS file extension

Visual C# Source Code File

Developer Files

BAT file extension

DOS Batch File

Executable Files

TIFF file extension

Tagged Image File Format

Raster Image Files

SYS file extension

Windows System File

System Files

THM file extension

Thumbnail Image File

Raster Image Files

ICNS file extension

Mac OS X Icon Resource File

System Files

CER file extension

Internet Security Certificate

Web Files

PCT file extension

Picture File

Layout Files

HQX file extension

BinHex 4.0 Encoded File

Encoded Files

CGI file extension

Common Gateway Interface Script

Executable Files