Windows are areas of the screen that behave as if they were independent terminals
in their own right.
A window can usually contain text or graphics, and can be moved or resized. More than one window can be on a screen at once, allowing separate tasks to be visible at the same time. Users can direct their attention to the different windows as they switch from one thread of work to another.
If one window overlaps the other, the back window is partially obscured, and then refreshed when exposed again.
Overlapping windows can cause problems by obscuring vital information, so windows may also be tiled, when they adjoin but do not overlap each other. Alternatively, windows may be placed in a cascading fashion, where each new window is placed slightly to the left and below the previous
window. In some systems this layout policy is fixed, in others it can be selected by the
user.
Usually, windows have various things associated with them that increase their usefulness. Scrollbars are one such attachment, allowing the user to move the contents of the window up and down, or from side to side.
This makes the window behave as if it were a real window onto a much larger world, where new information is brought into view by manipulating the scrollbars.
There is usually a title bar attached to the top of a window, identifying it to the user, and there may be special boxes in the corners of the window to aid resizing, closing, or making as large as possible.
In addition, some systems allow windows within windows. For example, in Microsoft Office applications, such as Excel and Word, each application has its own window and then within this each document has a window.
It is often possible to have different layout policies within the different application windows.