Gtk,gtk+, QT is a graphical interface development library (GUI Toolkit) that users can use to write GUI applications, where GTK + is an upgraded version of GTK.
Kde,gnome,unity is a desktop environment under Linux, where KDE is developed using QT, and GNOME is developed using GTK +. A desktop environment typically has a set of utilities, window managers, and design specifications to create a unified desktop. Unity is a gnome-based desktop environment for canonical, which uses some of the GNOME's utilities (Nautilus, Rhythmbox, etc.) and is used in the Ubuntu operating system.
Reference:
1, Https://askubuntu.com/questions/249150/what-is-kde-gtk-gtk-qt-and-or-gnome
2, Https://zh.wikipedia.org/wiki/Unity_ (%E4%BD%BF%E7%94%A8%E8%80%85%E4%BB%8B%E9%9D%A2)
3, Https://zh.wikipedia.org/wiki/GTK%2B
GTK, GTK +, Qt, KDE, GNOME, unity differences and connections