In recent years, fans and media seem to have blurred the line between rumor and pure speculation. For example when someone figures that since McNabb is from Chicago and since the Bears need a QB then McNabb would be a good fit there... that's speculation. Not a rumor.
When someone figures that since Vikings head coach Brad Childress was McNabb's QB coach and offensive coordinator and since the Vikes need a QB then McNabb would be a good fit there... that's speculation.
Now, when someone reports that there's been talk in the Ravens organization about putting together an offer for the Eagles for McNabb... ok, call that a rumor.
Overall though, I think ESPN's Michael Smith puts it best when calls the McNabb rumors, "more speculation than substance"