GTK (The Gimp ToolKit) is a relatively easy to use graphics package. It was originally written for and used by the GIMP, GNU Image Manipulation Program, and since then has become one of the most widely used graphics packages on a UNIX platform.
If you have never used GTK before, particularly if you've never used any graphics package before, it is recommended that you do the ``Getting Started'' chapter of the PyGTK tutorial, found here.