Say you found a pic on google. You like this pic. You want to post it to the good ol' TBBS. So you click on the pic in google, and copy the url of it to post it in a picture thread. You would therefore be 'hotlinking' it; using someone else's site (and bandwith) who is hosting that pic.
Instead, when you want that pic to post here, you need to right click save and host it on photobucket, or another site that is yours.