Orbs: tight vs. wide aspects
An orb is the allowable deviation from an exact aspect angle. A perfect square is exactly 90°, but a square with an orb of 5° (85° or 95°) is still valid -- just weaker. The tighter the orb, the more powerfully the aspect manifests in life.
Tight aspects (0-2°) are the most powerful. They dominate the chart and define core personality traits. These are aspects you feel every day. Medium orbs (3-5°) form the background of character -- noticeable but not overwhelming. Wide orbs (6-8°) are subtle influences that activate only during transits or progressions.
The Sun and Moon are given larger orbs (up to 10°) because they are the most powerful luminaries. Other planets typically use orbs of 6-8° for major aspects. Minor aspects require tight orbs of 1-2° to be considered significant.