Having attended this forum for several years not, I am beginning to understand some more about the products discussed and techniques shared. So I think I have an answer to my own question....
What is the difference between "sample libraries" and "virtual instruments?"
Maybe my answer is off, or too simple, but I think that sample libraries (for which I own several collections now) are purchased to be used in sample playback engines such as gigastudio (which I own but hardly ever use) or Kontadt and......... Virtual instruments are libraries that plug directly into notation programs such as Finale and are played through Finale. For instance, I have GPO and JABB that I can play back easily while in Finale.
So, what am I missing here on these terms? I'm just trying to learn the lingo.