Aspect type
The square aspect
A square is the quarter-turn between two planets, counted while they sit close to it. That angle and that margin are the whole of the definition; everything written about squares beyond them, this page included, is interpretation laid on top of a measurement.
The interpretation, then, and not the definition: two planets at right angles want incompatible things at the same time, and neither gets to finish its sentence. It is the aspect most often called difficult, and that word does it no favours. A square produces work. What it rarely produces is stillness.
Why friction is not damage
Planets in easy contact tend to agree, and agreement is comfortable and quiet. A square denies that comfort, so the two faculties keep negotiating, and the negotiation is where competence comes from.
Charts with prominent squares often belong to people who are unusually good at the thing the square is about. The skill was not a gift. It was the settlement.
None of that is in the definition, and none of it is a rule. It is a pattern worth watching for, which is a smaller claim and a more honest one.
What changes the reading
The margin matters as much as the angle. A contact sitting at the far edge of the 6-degree allowance behaves very differently from one that is nearly exact: nearer to exact is louder and harder to ignore.
Which two planets are involved changes everything else. A square between two fast-moving planets is a daily argument; one involving a slow planet is a long season.
A square is also not a verdict on a chart. It is one relationship inside a set of them, and the rest of the set has a vote.