Transit
A transit is the aspect a planet in the sky right now makes to a position in a birth chart, and it is the main way astrology describes timing.
The birth chart does not move; the sky does. When transiting Saturn reaches the degree of a natal planet, the tradition reads it as that part of the chart being tested, and the slower the transiting planet, the longer the period.
Speed is what separates a transit worth noting from one that passes unnoticed: the Moon crosses a natal point every month, Pluto perhaps once in a lifetime.
Frequently asked
How long does a transit last?
From hours for the Moon to a year or more for the outer planets, and longer when retrograde motion brings a planet back over the same degree.
Do transits predict events?
We read them as timing and tendency. Nothing in our reports claims an event will happen.