Shutter drag / Dragging the shutter
Shutter drag is slowing the shutter speed down to allow more ambient light to hit our sensor. Here's a couple of instances where this can be beneficial; an ocean. Dragging the shutter in this situation will allow more motion to be captured in our shot, making the water become more 'milky' and blurred. Nightclub/wedding receptions are another brilliant use of shutter drag. Dragging the shutter and moving the camera slightly, when using a flash in rear curtain mode, captures movement in the lights present and makes for some super interesting photos!