Each year, the planets in our solar system are in constant motion. As a result of this constant motion, at given times every year, these planets move from one sign to another, and in the process form significant angles to each other and to the planets in your individual birth chart. These planetary movements are referred to as "transits."
When a transit involves the formation of a major angle (aspect) between two planets, it can have an effect on both the collective and/or individual, depending on the planets involved. Because the outer planets move at a much slower pace than the inner planets, these transits represent more long-term cycles of development.
Transits vary depending on the year, but there are typically 3 exact "hits," or moments in time when the angle between the two planets becomes exact by degree, when a transit of an outer planet occurs. Aspects between the "outer planets," or those furthest from the Sun will typically have larger societal effects, the impacts of which we may not even fully grasp until much later in the future.
Whether or not an individual will feel these transiting aspects depends on the degree of the sign the transit falls in and whether these degrees correlate with a person's natal planets or other sensitive points in their chart. This is the reason why some "feel" a particular transit on a personal level than others.