'Hotlinking is a term used on the Internet that refers to the practice of displaying an image on a website by linking to the same image on another website, rather than saving a copy of it on the website on which the image will be shown.' - Wikipedia.
Basically, it's directly copying and pasting and image URL whilst you should use a website like TinyPic or Photobucket.
Oh thank you! I've been thinking of making one but I'd have to decide fully on what I want to make and what kind of time I'd have. As you can see by this late reply, I haven't been on BI as much as I'd like