Pluto is a very dark, cold, slow (dwarf) planet, and is the furthest known planet from our Sun, visible only with a powerful telescope. It was only recently discovered, in 1930. Unlike other faraway planets, Pluto is not gaseous: It has a sold body.
Pluto takes 245 years to orbit the Sun. It is quite eccentric in that its orbital plane is tilted by about 17° off the ecliptic, unlike the orbital plane of other planets. This creates a strange effect as Pluto circles around the Zodiac, because it spends much longer in some parts of the Zodiac than in others. For example, it takes thirty years to travel through Taurus, but only fourteen years to make its way through Scorpio!
From Earth’s perspective, Pluto appears to be retrograde 54% of the year, which makes the retrograde somewhat insignificant in itself. However, the stationary position of Pluto -- when it seems to stand still as it changes directions -- is when the qualities and characteristics of Pluto are likely to be very noticeable.
During a retrograde period, we are often forced to step back and pause in our own evolutionary processes. The stations and retrograde periods of Pluto give us a chance to stop and consider our situation and the next course of action.
The Pluto Return occurs outside of the human life span, so we look to other points in the cycle for significance, such as the Pluto square which often indicates a time of mid-life changes and turmoil.
However, because of Pluto's eccentric orbit, it’s not always a mid-life thing: The square can happen as early as age thirty-seven and as late as age ninety-two!