In Data Integration what is the difference between Target Period Year and Target Year?

Summary:

In Data Management/Data Integration, what is the difference between Target Period Year and Target Year in Period Mappings?

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I figure this question is pretty straight forward and I'd just like to know the difference for my own knowledge and benefit, but I can't seem to find a definitive answer anywhere, even in the documentation. What is the difference between the Target Period Year and Year Target columns in the Period Mappings? Is there a scenario where you would need one and not the other, or a scenario when you'd need to populate both fields and they would not match? I'm assuming this has something to do with Fiscal Years that don't align with calendar years, but I'm not