Descending order reverses the key direction so the largest key comes first.
largest first
Reverse the score direction
The first score is now 30.
first score=30
Ordering examples are tiny finite table transforms; SQL dialects, NULL ordering, collations, indexes, optimizer behavior, performance, and product behavior are out of scope.
Same rows, new order
The base table stays the same; only the ordered output changes.
rows are reordered
Summary
Direction is part of the authored order specification.