The term "massive star" is not defined until late in the article. It should be done earlier (perhaps in the lede), and I'll try to find a way to do it. The term "massive" is also sometimes just used as an adjective (eg "stars less massive than 0.25 solar masses" or "one of the most massive stars known" and sometimes to refer to a class of stars (massive enough to go supernova  the conventional definition). This latter class is finally defined at the end of Solar System#Mass, but was used many times before that.
An edit was reverted, presumably because it looked like an edit of someone else's comment due to the change in IP. —Alex ( | talk | contribs)