Close call. It's easy to imagine how much worse this could've been. As always, drive safe, and don't get too anxious when behind slower folks - take a moment to smell the roses and be sure to pass with care.
"Tractor" is often used to describe all manner of motorized vehicle who's primary function is any work other than passenger transport. So a bus would not be a tractor but a big truck that tows trailers all day long would be. I've always heard them referred to as tractor trailers.