GDK is, as I understand it, the layer below GTK+. Sort of like the glue between X and GTK+, it handles stuff like graphics contexts and colormaps and such. Well, drawing, pretty much. It stands for the "GIMP Drawing Kit".

this nodeshell rescued by the bored gtk+ developer who can't seem to figure out how to write a simple gdk-based sprite engine that doesn't segfault at the moment rescue team. yeah, we're pretty specialized.