What is the difference between 'non voluntary' and 'involuntary' in Aristotles' philosophy?

My teacher divided actions into two pieces: voluntary action and not voluntary one. And he divided again the letter one, not volunatry thing into NON-voluntary and IN-voluntary one, saying that two things are actually different.

But I don't undertand what is the difference between them.
What makes them different?

I'm questioning this in terms of Aristotles' philosophy.