_reverse

Produces the same Collection it receives, as a List, in reverse order -- Function
Anything -> _reverse -> The same Type
Receives
A List of any sort
Produces
The same List, in reverse order
This does exactly what it sounds like: it produces the same list, in reversed order.
_reverse can technically be used on any Collection, but is only useful for Lists. However, it can be useful after sorting a Set:
SET -> _sort -> _reverse
You can't _reverse a Set itself (Sets have their own intrinsic order), but _sort always produces a List.