Moving backward in the rotating reference frame of the Earth. In other words, it's rotating slightly more slowly than the Earth as a whole.

Paper: Inner core backtracking by seismic waveform change reversals (11 points, 21 days ago) https://news.ycombinator.com/item?id=40679957

I wonder if that has any effect on the periodic flipping of the north and south magnetic poles. Something has to cause that to happen.