A motion photo is a photo file that includes not only a still photo, but also a few seconds of video leading up to the still photo.
Why would I take a motion photo?
Motion photos capture your photo, plus something extra: that magic smile, that silly dance, or that sly wink.
Motion photos also allow you to capture a shot that you might have otherwise missed. Imagine you are waiting for the perfect shot of a songbird, but suddenly the bird flies away. You missed your opportunity, right? Not with motion photos! You can go ahead and press the shutter button, capturing the past several seconds. Now you have about 90 frames of your songbird! It's like a time-travel machine!