Family History Through the Alphabet – J is for …file types

I have a rudimentary knowledge of file extensions, those (mostly) little three letter codes that append themselves to the end of our file names to indicate what type of files they are, or, as a dictionary says " The portion of a filename, following the final point, which indicates the kind of data stored in the file."  

I know that my family history files contain items with a number of  different extensions. Some of the ones in my collection are:

.avi   Audio Vidio Interleave

.csv  Comma Separated Values 

.doc  Microsoft Word Document

.ged  Gedcom Genealogy Data 

.html  Hypertext Markup Language

.mp3  MP3 Audio

.mp4  MP4 Video

.pdf  Portable Document File

.png  Portable Network Graphic

.ppt   Powerpoint Presentation

.rtf    Rich Text Format

.tif    Tagged Image File

.xls   Excel Spreadsheet

.zip   Zipped File

The files bearing these extensions document my genealogy Journey.

My favourite file extension that is on over 90,000 of my files is: 

.jpg  JPEG Image 

What is the extension of your favourite file format?