A Station is when a planet changes direction from direct to retrograde, or from retrograde to direct. Astrologically, a planet's energy is extremely intensified for at least a day, often up to a week, when it becomes stationary. The planet's energy is powerful and dominant.
Think of a pendulum as it swings. When it reaches one side, it slows down and pauses (becomes stationary) and then starts to go the other way. In the same way, a planetary station is when a planet slows down and seems to hover around the same degree, and then resumes motion in the opposite direction.
When a planet pauses and changes direction like this, it is called a Planetary Station. We say "Mercury is making a station" or "Venus is stationary."
When someone is born within a few days of a planetary station, that planet becomes very strong in their chart, often seeming to "take over the chart." When a planet stations by progression, it can be a significant turning point in the person's life, particularly relating to where the planet is located in the natal or progressed chart, the house(s) it rules, and so on.
See also my article series on Retrograde Planets, including an article specifically about planetary stations.
