Final answer:
An assisted conversion is when a user's interaction with one traffic source contributes to a conversion that eventually occurs through a different traffic source.
Step-by-step explanation:
An assisted conversion in the context of digital marketing analytics refers to the scenario where a user interaction with a particular traffic source did not directly result in a conversion, but played a role in the conversion path and ultimately led to a conversion during a subsequent visit that may have come through another traffic source. Specifically, option b: "When one traffic source results in a later goal completion through another traffic source" is the correct definition of an assisted conversion. For example, a user may click on a display ad (first interaction), then leave the site, but later return through an organic search and complete a purchase. The initial display ad interaction is credited with an assisted conversion because it contributed to the final conversion action.