The most common graphical user interfaces use the desktop/ workspace and the windows metaphor.
Desktop
A desktop/ workspace corresponds to a big area in the available screen space whence applications are launched, and within which statuses, widgets and windows are displayed.
There may be multiple workspaces on a device - especially in case of devices with limited screen size.
Layering
Various windows, widgets and the desktop conceptually form a stack of various displays available to the user. This concept is useful when understanding widgets.
Taskbar, statusbar
A narrow portion of the screen is sometimes dedicated to displaying the statuses of various running applications, outputs of widgets displaying info like time, weather etc..; and to provide place for menus to launch applications.
Windows
A window is an area of the screen which is dedicated as an input/ output interface. A window may be overlaid with another, or ’minimized’ to have 0 screen area - and the corresponding area available for interaction with the window is correspondingly reduced. A window may be fully closed, possibly resulting in the termination of the corresponding application.
In case of small desktop workspaces (as in pocket computers), the active window occupies all of the available area on the workspace.
Task switching
Switching between windows is done using a program called ’task manager’, which is generally invoked using the taskbar or special key combinations.
Views and perspectives
The Window is designed to be a collection of various views. Eg: Eclipse, RapidMiner. Perspectives are particular arrangements of certain views. UI’s often allow (re)definition of perspectives by moving or adding views.
Widget
A widget is a window which is always on the layer immediately above the desktop. So, whenever one views the desktop, the widget is necessarily seen on top of it. Unlike windows, they usually don’t have simple means to close them.