Hotlinking (hot linking):

Also see:
Definition of "Direct Linking"
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Free Hotlinking Checker - Test Your Hot Linking Protection

"Hotlinking" (also called "hot linking", "leeching", and "bandwidth theft") is a term referring to when a web page of one website owner is direct linking to the images or other multimedia files on the web host of another website owner (usually without permission, thus stealing bandwidth).  This not only causes the other person to pay for the bandwidth of the hotlinked file, but often is intellectual property theft.  The term is also used loosely (a misnomer) by free image hosts which allow you to store images on their server and allow you to direct link the hosted image files on forums or other websites (sometimes altering the image to have a watermark).  One of the most common occurrences of "hot linking" is when people are forum posting and they hotlink pictures from another website to use as avatars or signature images on the messageboards (forums).  Some disadvantages of hot linking worth considering are that the webpage generally loads slower when you link to images stored on a different web hosting server than the webpage is hosted on, and the owner of the image has full control to disable hotlinking, or delete, rename, or worse yet, do a "switcheroo" (i.e., switching the file name to be another image which is sure to cause the hotlinker embarrassment) of the hot-linked image.  Common methods of preventing hotlinking are by using an .htaccess file, using the "Hotlink Protection" offered in control panels such as Cpanel, or simply renaming image files periodically.