Transits refer to where the planets are now in "real time" (as opposed to planets in your natal chart).
Transits also refers to a forecasting technique used by astrologers, in which the transiting planet positions are compared to where they were when you were born (in your natal chart). When transiting planets form aspects to your natal planets, or move through a house in the natal chart, this activates those natal energies in your life. A transit might have minor day-to-day effect, or a major and life-changing effect – which usually depends on the speed of the transiting planet; slow planets usually have a more significant or profound effect on your life.
Major effect: Uranus, Neptune and Pluto transits usually leave your life very different than how they found it, taking you through a deep transformation and major change. The effects tend to reach you at a "soul" level. The effects of each transit last about a year, sometimes two.
Medium effect: Jupiter and Saturn transits are also significant and can be life-changing, but tend to affect you more on a societal or achievement level, rather than a "soul" level. The effects of the transit can last roughly from one to nine months.
Minor effect: The Sun, Moon, Mercury, Venus and Mars all move so fast that their effects typically last only a few days at most. They tend to affect us on a day-to-day basis at a more ego-based level. The exception to this is when Mercury, Venus or Mars go retrograde, which may bring a longer-term process of growth lasting a few weeks to a few months. That said, transits from these fast-moving planets can sometimes trigger events and turning points in the longer process of growth brought by the slow-moving planets.
