The Mix

First of all, I think this is my first post. Thanks for the wonderful forum.
Now my question. I feel dumb asking this. I've searched all over the forum and have not found this simple answer.
When I read about "the mix" I've seen people say to use polyurethane varnish. My understanding is that varnish and polyurethane are not the same. Many people simply call all wood finishes varnish by default.
So when I go to buy ingredients for "the mix" am I looking for any clear wood finish on the shelf that says its oil-based poly?
I'd assume I should get an exterior finish, not an interior finish. What about interior/exterior poly finishes?
Thanks!
Now my question. I feel dumb asking this. I've searched all over the forum and have not found this simple answer.
When I read about "the mix" I've seen people say to use polyurethane varnish. My understanding is that varnish and polyurethane are not the same. Many people simply call all wood finishes varnish by default.
So when I go to buy ingredients for "the mix" am I looking for any clear wood finish on the shelf that says its oil-based poly?
I'd assume I should get an exterior finish, not an interior finish. What about interior/exterior poly finishes?
Thanks!