Retrograde
In plain words
When a planet appears to go backwards through the signs. It is not really reversing — we are overtaking it, the way a slower train seems to slide backwards when yours pulls away.
In the tradition's terms
Apparent backward motion, an artefact of the relative orbital velocities of the Earth and the body.
In depth
The station points bound the retrograde arc. A slow body crossing a natal degree while stationing will perfect the same aspect three times, and the tradition reads those three passes as a beginning, a reconsideration and a settling.