It's not a group layer with a folder icon if that was your first thought, it's an inset layer with a downwards pointing arrow in front of it above a dominant normal (not inset) layer. But how do you make these special layers? what do they do or mean exactly? what are they even referred as for that matter?
I enclosed a screenshot of a file I saw this on and if you look in the layers window on the right you'll see what I'm talking about. I have spent far too long trying to figure out how to do that, or at least figure out what it indicates. I even looked through my CS3 photoshop bible only to see zero mentioning of this.
Has anyone here worked with these before?