A widget toolkit, widget library, or GUI toolkit is a set of widgets for use in designing applications with graphical user interfaces (GUIs).
A widget toolkit, widget library, or gui-toolkit is a set of widgets for use in designing applications with graphical user interfaces (guis).
The toolkit itself is a piece of software which is usually built on the top of an operating system, windowing system, or window manager and provides programs with an application programming interface (api), allowing them to make use of widgets. Each widget facilitates a specific user-computer interaction, and appears as a visible part of the computer's GUI. Widget toolkits can be either native or cross-platform.