A brush is kind of like a stamp that you stamp onto icons. You can download them for certain programs like Photoshop or Paint Shop (which I use). Like in icon 32 at the bottom left is a little design that I "stamped" or "brushed" onto the icon. Or the swirl on the right of the icon I am using right now. I hope that helps and you can get some great brushes at 100x100_brushes