GTK (GNU Widget Toolkit) is a widget toolkit common in Linux and
modern Unix environments. It is freely-licensed under the terms of
the GNU GPL, and used to create notable programs such as GIMP,
Mozilla Firefox, and Pidgin.
AWT (Abstract Widget Toolkit) is a widget toolkit used by many
Java applications.The widgets themselves normally take on
characteristics of widgets from the host operating system (be it
Windows, Mac OS X, or Linux), though it can also use Swing to
provide its own user interface.
When used in conjunction with each other, it probably refers to
libraries used by the Java program to provide a GTK look and feel
on a Linux or Unix system.