Panning is a photography technique that’s typically associated with “real” cameras, at least the ones that let you control the shutter speed. Smartphones traditionally didn’t allow users to fiddle with that setting.
But, thanks to apps like Slow Shutter Cam, the panning technique can be achieved.
After using it during my recent trip to DC, it seems as if the longer shutter speed is being simulated since you can also control how much blur you want. I found the best results came from using shutter speeds at the faster end of the spectrum (i.e. 1/4 or 1/2 second) while varying the blur strength based on your goal.