Long Exposure is another new Live Photo effect. It essentially considers the whole Live Photo video clip as one big exposure.
Its results can be mixed and the feature is best used on images where only parts of it are moving – think a running stream.
The result is that your device will essentially blur this part of the image creating a unique look.
To use it, take a Live Photo, find it in your Photos, swipe up from the bottom and then choose the option Long Exposure.