That portion at the end of the filename that describes its file type is called File Extension. It can be from one to several characters long and can usually be identified easily since the filename and the file extension are separated by a "." just like for example "cars.avi" which means that the AVI part is the file extension. AVI file extension stands for Audio Video Interleave file. It enhances video data within a computer and stores compressed video files. Its related program is the Windows Media Player, which plays compressed video files within AVI files, however, correct codecs must exist within a computer to enhance the operation of the file. There are various codecs used by the file and this includes DivX, DV, MJPEG, Indeo and YUY2 codecs. And Audio codecs are also used by AVI file extension aside from the video codecs. This enhances sound of the video file or data. Examples of audio codecs are MP3, PCM and more. The developer of AVI file extension is the Microsoft Corporation which is also the author of worm and trojan programs that create virus program that is related to AVI file. That's why this puts one at risk of infection when downloading this file. So, one must be careful when downloading this file from the internet.
There are a lot more of different types of file extension widget and different applications are required to open different types of files. The information about file type associations and the applications which are allowed to open them is stored in windows registry. And this website contains a comprehensive database of file extension. The information they provide in each file extension is brief and to the point. Each entry they have contains information about the format, the creator, the description of the file, and the related applications of the file extension and also its common path .