1. Actually an optical illusion, a planet is called retrograde when its course appears to turn backward. When a planet is in retrograde motion at one’s birth, its energy is turned inward and must be developed from an inner awareness before it can be fully expressed externally.
SOURCE: The Truth About Astrology, Gloria Star
2. From our viewpoint on earth, planets other than the Sun and Moon appear to back up at certain times of the year. They aren’t really moving backwards but appear to be moving backward in the zodiac from an earthly perspective.