Originally described for Internet Mail. Now also used by Web.
Describe type and format of contents. Allow browsers to automatically call
appropriate plug-in (the software which will display something 
within a browser) or helper application (the software which will display
in something in separate window). Popular MIME
types (Content-Type):
- text/plain -- plain, unmarked text
 
- text/html -- text with HTML mark-up
 
- text/xml -- XML markup
 
- image/jpeg -- JPEG picture
 
- application/pdf -- Portable Document Format file
 
- application/octet-stream -- unstructured binary data to be saved.
 
- video/mpeg -- video
 
- video/quicktime -- video
 
- audio/x-wav -- audio
 
- application/x-www-form-urlencoded -- data from
   the form sent from browser to server for regular forms
 
- multipart/form-data -- data from
   the form sent from browser to server when you do file upload