I've heard of 'inverse' or 'interior' drifting, and same with exterior... I think it was to do with statistics or something... What's the difference and how does it affect gameplay?
Do you mean modifying your drift path?
You can do this by steering more to the left (or right) while you are already drifting.
For example, if you're drifting left, you can get a sharper drift by steering even more to the left, or a wider drift by steering to the right; lesser to the left.
(Of course, reverse the directions if you're drifting to the right)
Just note that you can only do this while having your drift mode set to manual.
The example below shows the difference in paths when doing a wide/sharp drift as compared to a normal drift to the right.