Orb
An orb is the tolerance around an exact aspect, the number of degrees within which two planets still count as connected.
A trine at exactly 120 degrees is rare; one at 117 is still a trine, within a three degree orb. Traditional practice varies the orb by planet rather than by aspect, giving the Sun and Moon the widest allowance.
The tighter the orb, the louder the aspect: our reports order aspects by exactness for that reason, and they print the orb beside each one so the reader can weigh it.
Frequently asked
What orb should I use?
There is no single answer. Traditional sources assign orbs to planets, modern practice often to aspects; we print the measured orb so either reading is possible.
Does a wide orb mean a weak aspect?
Generally yes: the further from exact, the quieter the connection.