The term task pane is used by Microsoft to identify any area cordoned off from the main screen area of an application and used for a specific function, such as changing the displayed font in a word processor.[2]
Three-pane interface
A Three-pane interface is a category of graphical user interface in which the screen or window is divided into three panes displaying information. This information typically falls into a hierarchal relationship of master-detail with an embedded inspector window. Microsoft's Outlook Expressemail client popularized a mailboxes / mailbox contents / email text layout that became the norm until web-based user interfaces rose in popularity during the mid-2000s. Even today, many webmail scripts emulate this interface style.