Retrograde
When a planet appears, from Earth, to move backward through the zodiac for a while — an optical effect of two orbits at different speeds.
Retrograde motion is an appearance, not a real reversal: every planet keeps orbiting the Sun in the same direction the entire time, but because Earth is also moving, a slower outer planet can appear, from our vantage point, to drift backward against the background stars for a stretch. It's the same effect as passing a slower car on a highway, which briefly looks like it's rolling backward relative to the roadside even though it never stops moving forward. Every planet except the Sun and Moon goes retrograde on a regular schedule; Mercury does it most often, about three times a year, for a few weeks at a time. The word describes a period, bounded by two stations, rather than a single day.