MIME Types

This is just like adding your own file extension in windows.

For example:
If you have a piece of software that outputs a text file but doesn't use the .txt extension, you can still store it on your web space with out altering the extension, you just add the extension as a MIME type, copying the MIME information from the .txt one.

So if I had text files with the extension .zzx i would enter text/plain in the MIME type box and zzx in the extension box, and from now on the web server will treat these files as text files, and open them in the browser window, instead of offering a download.