1. A powerful, fast open source graphics library for the X Window System on UNIX/Linux, which is used by programmers to create buttons, menus, and other graphical objects. (Also, see Gtk/Gtk+ and KDE.) From I-gloss

2. At about that time, a new GUI library was released. It was called Qt and was developed by Troll Tech. It was not free, but it was an outstanding technical accomplishment in that it worked efficiently and cleanly on many different platforms. It was shunned by some factions of the Free software community because it was written in C++, [Which is not considered to be the standard development language by the Free Software Foundation because it is not completely portable and possibly for other reasons.]and was only free for noncommercial applications to link with. Nevertheless, advocates of Qt went ahead and began producing the outstanding KDE desktop project--a set of higher-level development libraries, a window manager, and many core applications that together make up the KDE Desktop. The licensing issues with Qt have relaxed somewhat, and it is now available under both the GPL and a proprietary license. From Rute-Users-Guide

3. Qt is a GUI software toolkit which simplifies the task of writing and maintaining GUI (Graphical User Interface) applications for the X Window System. Qt is written in C++ and is fully object-oriented. This package contains the shared library needed to run qt applications, as well as the README files for qt. From Redhat 8.0 RPM