The words a chart uses
What are aspects in astrology?
An aspect is an angle between two points in a chart, such as a square of ninety degrees, which the tradition reads as a relationship between their themes.
Two planets are always some number of degrees apart along the zodiac. When that distance comes close to one of a few angles, the tradition calls it an aspect and reads the two planets' themes as being in conversation. How close counts as close is the orb: a few degrees either side of the exact angle.
The major aspects
A conjunction (0 degrees) is traditionally read as two themes blended, hard to tell apart. An opposition (180 degrees) is read as two themes facing each other, each showing the other more clearly. A square (90 degrees) is read as friction between two themes, often a source of effort. A trine (120 degrees) is read as ease between them, sometimes so easy it goes unnoticed. A sextile (60 degrees) is read as an opening that may ask for a step to use.
The quincunx (150 degrees) is a minor aspect, read as two themes that do not easily see each other and ask for adjustment.
No aspect is good or bad
A square is not a misfortune and a trine is not a reward. Friction can be where effort and skill grow; ease can be where attention lapses. Becoming Choice describes each aspect with more than one way it might show up, and leaves room for none of them to fit.