When a planet is retrograde, it appears to go backwards in the sky.It doesn't really go backwards — it's an optical illusion because we're viewing the planet from Earth's perspective. All planets except the Sun and Moon go retrograde some of the time.
A retrograde planet travels in the opposite direction relative to the natural sequence of Zodiac Signs - for example, from Aries to Pisces to Aquarius, and so on.
Astrologically, when a planet is retrograde, its energy is internalised and intensified. It's often not easy to be objective about a retrograde planet's energy, or to work with it out in the world. It's a bit like trying to look at the under side of your chin!
For the outer planets (Mars through Pluto and beyond) it's a little like passing a car on the highway — it looks like the other car is moving backwards against the backdrop of the scenery.
In the case of Mercury and Venus, it's like watching someone on a merry-go-round or carosel. If you don't realize they're going in a circle, it looks like they go forward, then backward, from your viewpoint.
Pronounced: RET-trow-grade. See also my article series on Retrograde Planets.