What is GTK or xorg-x11-sdk?

[Dave Gutteridge]

I am trying to configure and make a driver (wacom) which seems to 
require something called "GTK". I looked around the internet for what it 
is and if there were RPMs I could download. However, I couldn't 
determine exactly what it was. It seems to have something to do with 
Xorg, and I thought I saw there was a YUM repository called 
xorg-x11-sdk, but I'm a bit confused. Is GTK a development environment 
for the Gnome desktop?

The wacom driver builder will not make a wacom.o or wacom.ko file 
without GTK, or so it seems.

Dave