Aspects
Orb
How close an aspect needs to be to count - the margin of influence.
An orb is the degree of allowance given when determining if an aspect is active. For example, a conjunction (0°) might be considered valid within an 8° orb, so planets at 2° and 9° of the same sign would still be conjunct. Tighter orbs (smaller numbers) indicate stronger aspects. Different astrologers use different orb standards.
Example
Sun at 15° Aries and Moon at 20° Aries are 5° apart - within most conjunction orbs, making this a valid Sun-Moon conjunction.