Within most Astro tools is a property referred to as Orb. The Orb controls the amount of variation allowed for a result to be considered as passing / being true.
For example, if a Planetary Aspect for Mars and Venus was set to Square, without an orb value the indicator would only display when the angle is exactly 90 degrees.
Planetary Aspect - Mars / Venus - Square - No Orb
The orb value (2 by default) allows us to add a buffer either side of the 90 value, so that any value between 88 and 92 will display the aspect.
Planetary Aspect - Mars / Venus - Square - With an Orb Value of 2
Some tools will show a shaded zone for the orb, and a vertical line to indicate the date of the exact match.
</span>The Orb properties for Astro tools are split into an Orb for Longitude and an Orb for Latitude.
This allows tools to combine Aspects which use Longitude and Latitude in a single tool, rather than having to keep them separate (as Latitude orbs are usually require a much smaller value).