The device is unable to tell you how it is being held.

The device is being held in portrait mode.

The device is being held in landscape mode.

Web Page Orientation with HTML and CSS Media Queries

You can now use CSS Media Queries within your HTML Web Page to distinguish which orientation the browser is currently set to.

This is mostly aimed at mobile and tablet browsers, where users can either hold the device in an upright, portrait way, or on its side, in a landscape way.

By being able to target which way the browsing device is being held, you can provide a web page layout that is better suited for the use in hand.