What does the term "Retrograde" mean by the way?

Retrograde sounds a "hi-fi" astrological term as far as planets are concerned. What does that mean actually?
Any planet which is retrograde, just stops on its path for a while. ( thus creating a havoc on us, the dependent mankind !) But, let us not forget
that strong ruling planets in our Birth-chart in fact benefit by this retrograde behaviour or stopping of the planets in their path.
On an additional note, Sun & Moon never turn retrograde..whereas, Rahu & Ketu ALWAYS move reverse / retrograde!