What is a "reversed" opening?

Is it simply an opening in which the moves are played in the reversed order? Or does it mean that it is an opening normally played by Black, but instead it is played by White?

Thanks.

The latter. For example, from the English 1. c4 you can get into a "reverse Sicilian" with 1... e5. In principle, the game can play out along the lines of the Sicilian with the extra consideration that the "defending side" now has an extra move. Some of the concepts of the classic Sicilian can apply, but the extra move can allow some new tricks.

My favourite reverse system is 1) Nf3 where the King's indian defence can reverse into the King's Indian attack but I have tried a number of things over the years - like 1) e3 or 1 d3) where 1)...e5 allows 2) c4 for a reverse sicilian.