The word everyone hears and nobody explains
Most people run into the word transit the same way. Somebody tells them Saturn is transiting their seventh house, or Pluto is making a transit to their Moon, and the sentence sounds important but means nothing because nobody stops to explain the mechanism underneath.
The mechanism is simple, which is maybe why it gets skipped. Your birth chart is a fixed record of where every planet stood at the minute you were born, frozen there permanently. But the actual sky kept moving. Right now every planet in it sits at some degree of some sign, somewhere different from where it was the day you arrived. A transit is the moment when a planet in today's sky lands on a point that matters in your permanent chart. That is all it is. The moving sky touching the still picture.
What makes it worth a whole article is what that touch tends to do. A slow planet arrives at a sensitive point in someone's chart, sits there for months. The area of life connected to that point starts demanding attention in ways the person cannot ignore. Nobody schedules it. It shows up anyway.
Speed is everything
The Moon crosses the full zodiac in about a month, spending a few hours on any given degree. A Moon transit is a passing mood. By the time you have noticed it, the Moon has moved on and you feel different again.
Mercury, Venus and the Sun work at a similar pace, days instead of hours. Their transits give a stretch of days its flavour and then leave.
The outer planets are where it gets serious. Jupiter takes roughly twelve years to go around the chart. Saturn takes about twenty-nine, which is why the Saturn return, Saturno coming back to its natal spot near age twenty-nine, is the slow transit people know best even if they do not call it that. The three modern planets move slower still. Uranus (discovered in 1781) takes around eighty-four years. Neptune (1846) and Pluto (1930) are slower again. When one of those parks itself on a point in your chart it can stay there, moving forward and backward over the same degree because of retrograde motion, for a year or more. The contact gets made three times or even five, spread across a long season that has a slow fade-in and an even slower fade-out.
This is why the transits that change lives are almost always the slow ones. They rarely feel like a single event either. They feel like a weather system that moved in and will not leave until something in you has shifted.
What an astrologer is actually looking at
When I sit down with a chart and its transits, two things tell me where to focus. The angle the transiting planet makes to the natal point and the part of life that point governs.
The angle, called an aspect, sets the tone. A flowing angle tends to open doors without much effort on your part. A tense one tends to apply pressure, the kind that makes you adjust something you thought was settled. I have never found either one to be simply good or simply bad. The flowing ones can pass without you doing anything with them. The tense ones are often where the most honest reckoning happens.
The house tells me which room of your life the transit walks into. The same planet making the same angle will show up as a career question in one person's chart and a relationship question in another's, because the point it touches governs a different area for each of them. That is why generic horoscopes, which can only go by Sun sign, miss the house entirely and end up vague.
If you have read the piece on the Saturn return, you already know one transit well. It is simply Saturn making a transit to its own natal position, the planet returning to where it started. Every retrograde you have heard worried about works the same way. They are all the moving sky touching the still chart.
What this will not tell you
Here is the part I care about most. It is also the part that gets most abused. A transit describes a quality of time, not an event.
The daily horoscope industry makes its living by blurring that line, turning "Saturn is transiting your tenth house" into "you will have a career setback in March." I have never seen it work that way. What I see is a period that keeps asking certain questions. The person answers them in their own way and on their own schedule. Two people living through the same Saturn transit can come out of it having made opposite decisions. The chart does not prefer one over the other.
The question worth asking about any transit sounds different from what most people expect. What part of my life is being asked to grow right now, and what kind of pressure is doing the asking. That question has an honest answer. What is going to happen to me does not. And the answerable one is usually the one that actually helps.
If you want to see your own transits, the free AstroVisor 3D viewer lets you build your chart and set any date to watch how the sky touches it. And if a particular slow transit is what brought you here, the articles on the Saturn return and on Saturn retrograde go through two of the most talked-about ones in detail.