Since the name change is so recent, you're likely to run across both sets of names.
+PLT/Racket stands to Scheme in something like the relation Firefox stands to HTML. It's one program among others for working with the language; and many of those programs (or web browsers) permit different extensions, have small variations, and so on.
+
PLT Scheme had several components. The two most visible components for us
were the command-line interpreter "mzscheme" and a teaching-friendly editor/front-end "DrScheme". In
Racket these have been renamed "racket" and "DrRacket",