Go to the following Foundation CSS framework documentation url:
http://foundation.zurb.com/docs/navigation.php
In the section named Nav Bar you will see an example for horizontal navigation bar. Now try to gradually minimize the browser’s window, when the window is minimized enough (to be like mobile devices resolution) you will notice that horizontal navigation bar is turned into vertical navigation bar. I need to know the technical definition for this behavior occurred to the menu.
I believe you are looking for responsive web design; which is design that adapts based on the user agent’s viewport.
Twitter’s bootstrap framework for example, has responsive design built-in.