What is a Windows 7 visual style?

Hi everyone, I hope you're doing well. If you've used Windows XP skins, you'll surely have noticed that Windows 7 themes change very little compared to those skins. Windows 7 themes only change the color of windows and the sounds, and make no other real changes. But Windows 7 has something else called a visual style, which transforms it completely and changes the look of everything. These visual styles usually come as installable files, and they're very beautiful and attractive.

In the picture below you can see one of these visual styles installed on my system:

As you can see, the title bar has an interesting bulge and the buttons have changed shape too. To download them you can go here, here and even here! Some visual styles that are very extensive and larger in size come as a full setup file, and it's worth installing some of them for a change.