Refers to a graphical dialog used to display important information to the user. These dialogs appear above all other content, blocking application flow until user input is received.
Modal windows are commonly used in GUI systems to command user awareness and to display emergency states. On the Web, they are often used to show images in detail.
Frequent uses of modal windows include:
Drawing attention to vital pieces of information. This use has been criticised as ineffective because users are bombarded with too many dialog boxes, and habituate to simply clicking "Close", "Cancel", or "OK" without reading or understanding the message.
Blocking the application flow until information required to continue is entered, as for example a password in a login process. Another example are file dialogs to open and save files in an application.
Collecting application configuration options in a centralized dialog. In such cases, typically the changes are applied upon closing the dialog, and access to the application is disabled while the edits are being made.
Warning that the effects of the current action are not reversible. This is a frequent interaction pattern for modal dialogs, but it is also criticised by usability experts as being ineffective for its intended use (protection against errors in destructive actions) due to habituation. Actually making the action reversible (providing an "undo" option) is recommended instead.
