Twilight is the name for this high energy music that seems to be a blend of hard non-cheesy full on and darker sounds.
This contains the South African sound, the portuguese sound (Tryon, Khopat, Sidhartha) and many others.
Many will argue about the term since you can still use Hard Full On, but IMO there's a huge diffrence.
Twilight artists use melodies that tend to be darker (hence Twilight), much more agressive bass than the regular full on and way harder and edgier sound. Although some track are difficult to distinguish between Full On and Twilight most Twilight tracks have their sound which is far away from the more mainstream sound of Full On.
I for example dislike Full On, but LOVE twilight.
Some examples of Twilight psy.
South African sound
http-~~-//www.youtube.com/watch?v=eAT1cyIOzYY
Portuguese sound
http-~~-//www.youtube.com/watch?v=hp-vjbjXe1M