In other words, this is when two planets are close to sharing an aspect between each other, but they're too far away to be within a reasonable orb. Ordinarily, these planets would not be considered in aspect to one another. However, if a third planet forms an aspect to both of them, that third planet can act as a bridge or "middle-man" that joins the other two planets and completes their aspect. This is called "Collection of Light."
This happened in the chart of the Full Moon in Aries on 9-Oct-2022. The Sun approached a trine aspect to Mars with an orb of 6:13 (6 degrees, 13 minutes), which is a reasonable orb for a trine. Venus was closesly conjunct the Sun (3:22 orb) and also applied to a trine to Mars, but their orb at the time of the Full Moon, 9:36, was too wide for them to form the trine on their own. However, since the Sun was trine Mars and the Sun was conjunct Venus, the Sun acted as the Collection of Light. Therefore, the Venus trine Mars energy was activated through the Sun's aspects to both of them.