The main window of an application, typically, is composed of a frame window and a client window. The frame window usually includes control windows such as a title bar, system menu, menu bar (action bar or menu in user terminology), and scroll bars.

A frame window provides the standard services the user expects from a window-for example, moving, sizing, minimizing, and maximizing. The frame window receives input from the control windows (called frame controls) and sends messages to both the frame controls and the client window.