Mars has been in retrograde motion recently as Earth has been overtaking it. Earth has a higher angular velocity. Mars is still going forward but looks like it is going backwards relative to a fixed reference point. OK, there are no fixed reference points in space but the background of stars are so far away that it doesn't make much difference. Here Mrs B was overtaking a lorry coming up to a bridge. Above, the cab lines up with a bridge in the distance.
In the second view there is daylight between the cab and the bridge and below the cab is nowhere near lining up with the bridge. You could achieve the same effect if we were still and the lorry went backwards. But all the while it was moving forward at 50mph. This is what we mean by retrograde motion.
