I assume this is the test with the highest number for AA.
So say you took it and your AA was 18 and you took it again and your AA was 20. They'll use the scores from the test with the AA being 20 to look at. Hope that helped and made sense!
Some schools may do this, there's no way to really know unless you call and ask. But generally when they say they consider highest overall score they mean AA. 🙂