Aspect
An angle between two points in a chart, measured in degrees, close enough to a round number to count as a real contact.
Planets sit at different points around the chart's circle, and an aspect is simply the angular distance between two of them, measured along that circle. Certain angles, like 0, 60, 90, 120 and 180 degrees, are read as meaningful contacts rather than coincidence, because they divide the circle evenly and keep showing up in how a chart's parts interact. An aspect doesn't have to be exact to count; a small allowed range on either side, called the orb, still counts as the angle being 'in aspect.' Aspects are the main language a chart uses to describe how its parts relate to each other, and they're also how a moving sky is read against a fixed birth chart, in Transits, or how one person's chart is read against another's, in Synastry.