The name of a Web site that frames another Web site. For example, when you do a search on Ask Jeeves and it calls up the Web site you found, the results come back in the lower frame while the Ask Jeeves logo and nav bar occupies the top frame within the same browser. That's a parasite. Many Web sites do this in an effort to make navigating easier, but it is a questionable practice for a couple of reasons: First, it actually makes navigating harder, since the back button is disabled; and second, parasites are republishing someone else's content without consent, and making it look like their own.
Frames are an excellent way to organize information on some Web sites, but most framed sites need a full screen and are not designed to have a parasite frame on top. The worst is when you get two frames inside a frame and then one of the frames repeats itself. Oy vey, there's no excuse for boguscode like that.