Hotlinking is when images on your account are being embed into another website, which does not own those files. The reason is that using hotlinking is basically an unauthorized use of the bandwidth of someone else. In order to avoid that you need to enter the following code into the .htaccess file on your account:

 

# stop hotlinking and serve alternate content
<IfModule mod_rewrite.c>
RewriteEngine on
RewriteCond %{HTTP_REFERER} !^$
RewriteCond %{HTTP_REFERER} !^http://(www\.)?domain\.com/.*$ [NC]
RewriteRule .*\.(gif|jpg)$ – [F,L]
</ifModule