What's a Modal Window?

In user interface design for computer applications, a modal window is a graphical control element subordinate to an application's main window. It creates a mode that disables the main window, but keeps it visible with the modal window as a child window in front of it. Users must interact with the modal window before they can return to the parent application. This avoids interrupting the workflow on the main window. Modal windows are sometimes called heavy windows or modal dialogs because they often display a dialog box.

Modal Window

I'm the modal window. You must interact with me to return to the page. Sometimes people will put intrusive things like a newsletter signup form in me to make sure people leave the website immediately and never return.