File Extensions – What are they?

All computer files have a short description to describe the type of file it is. The description is usually three letters long and is preceded by a full stop.  And it’s called a ‘file extension’.

Some of these file extensions are very common and well-known. For example, .doc – the DOC stands for ‘document’ and this is a Microsoft Word document.  Some are more obscure and although you are using these files all the time, you might wonder about the importance of those three letters after the dot in the file name.

Over the past couple of weeks on Facebook I have been posting about the types of file extensions and what they stand for.  Here, I’ve put them together in a handy list.


Txt stands for ‘text’. It’s a very simple format for any text, with no bold, italics or proper bullet points. The advantage of a .txt file is that it can be easily read or opened by any program that reads text.


PDF stands for portable document format. Produced by a company called Adobe, it enables you to send documents to people in a way that you can be sure they arrive in the style that you sent them. Also your document can’t be easily altered by the recipient.


WAV stands for Windows Audio format sound file, it’s called a wave file.  It is used for audio files. It’s not too popular for sending over the Internet, because the files can get too big.


MP3 stands for MPEG-Layer 3. This is a compressed audio file, it takes up a lot less room while only losing slightly on quality, and so is good for sending over the Internet.


MP4 stands for MPEG-Layer 4. This is a compressed video file.


WMV stands for Windows Media Video. This is also a compressed video file.


BMP stands for bitmap. The images you see when Windows starts up and closes, and the wallpaper that cover the desktop, are all in BMP format. These files tend to get quite large.


TIF stands for Tagged Image File Format. This is a type of image storing file popular with photographers and publishers.


JPG stands for Joint Photographic Experts Group. It’s pronounced jay-peg and written as either JPG or jpeg. JPG format is good for photographs, artwork, etc and is a compressed format so is smaller than the equivalent TIFF.


GIF stands for Graphics Interchange Format. It’s a compressed graphics file used to display images online. Often images on web pages are in GIF format, rather than JPG format, because a GIF file is smaller but is not suitable for photo images.


PSD refers to a PhotoShop Document. It can be edited in the PhotoShop program or a similar one such as GIMP. It allows more complex images to be created since many images can be layered on top of each other to create the effect you want.