…I’ve noticed some songs have a Chorus that is repeated and other songs have a Refrain that is repeated.
Is there a difference between a Chorus & a Refrain?
For example, in “Sitting On Top of the World,” there is a short part that gets repeated as “And now she’s gone…and I don’t worry
'Cause I’m sitting on top of the world.”
Is it a Chorus or a Refrain? Or is it two names for the same thing?
Silly answer: Maybe chorus expects others to join in while refrain need not??
I’ve always thought of refrains as a really short chorus, but it acts in the same way. The example you have with “Sittin’” or “Well roll on buddy” in Nine Pound Hammer would be refrains, in my mind, but it don’t hurt my feelings to call them a chorus.
Yes, I don’t know if you’d noticed but the spelling is different! 
Finally, a music theory answer I can understand!
I like that. It might not be accurate, but it makes sense.
Now @JohnM I find this funny - You folks with squeaky voices may REFRAIN from joining in. Crass I know
I find it funny too!
