When programming PHP-GTK applications and surfing through the manual, you will find some rather cryptic acronyms. Here is an overview of the more important ones.
PHP - PHP: Hypertext Processor - is a widely-used general-purpose scripting language that is designed for Web development and can be embedded into HTML.
GTK - the GIMP Tool Kit - is a library designed for creating graphical user interfaces. It runs on most UNIX-like platforms, on Windows, and on framebuffer devices.
GTK depends on several other libraries, among them GDK, Pango, ATK and GLib. The combined package is referred to as GTK+.
GDK - the GIMP Drawing Kit - is the abstraction layer that allows GTK+ to support multiple windowing systems. GDK provides drawing and window system facilities for X11, Windows, and the Linux framebuffer device.
Pango is a library for internationalized text handling. It centers around the PangoLayout object, which represents a paragraph of text. Pango provides the engine for GtkTextView, GtkLabel, GtkEntry, and other GTK+ widgets that display text.
ATK is the Accessibility Tool Kit. It provides a set of generic interfaces allowing accessibility technologies to interact with a graphical user interface. For example, a screen reader could use ATK to discover the text in an interface and read it to blind users.
Thanks to the ATK framework, GTK+ widgets have built-in support for accessibility.