Your device rotates to landscape when you turn it sideways and goes back to portrait mode when you hold it vertically.

Instagram just introduced one of its most significant changes in recent memory — landscape and portrait modes for photos and videos.

With the iPhone 6 Plus, 6s Plus, and 7s Plus, you have the ability to use the home screen in landscape mode (with the iPhone held horizontally) or in portrait mode (the iPhone held vertically ...

Thanks to iOS 15.4, your iPad’s volume controls will finally make sense in portrait and landscape modes.

Video should be shot and viewed in landscape mode -- that's the "long way" instead of the "tall way," the orientation that mimics your HDTV screen.