MIMEtypes

A MIMEtype is a universal method of associating a specific “kind” of file to a specific category of application.

For example, if you have an .mp4 file, you can be fairly confident that the file contains video, and so you probably want that file to be opened in a video player rather than, say, a word processor. You might think it logical to associate that file with VLC, a popular video player, but what if you don't have VLC installed? After all, there are several very good video players, and it would be better if the mp4 file would just open in some video player that can handle mp4 files.

The way this is accomplished is that files are assigned, on a systemwide level rather than a per-file basis, MIMEtypes based on their suffix.