Which term relates to the idea of initial evidence or assumption?

The correct term that relates to the idea of initial evidence or assumption is "prima facie." This term originates from Latin, meaning "at first face" or "on its face." In legal contexts, it is used to denote evidence that is sufficient to establish a fact unless disproven by further evidence. When something is established as prima facie, it means there is enough evidence to support an assumption or claim until evidence is presented to contradict it. This concept is fundamental in legal proceedings, as it creates a starting point for evaluation and further investigation.

In contrast, the other terms do not convey the same notion. "Pro bono" refers to professional work undertaken voluntarily and without payment, often to benefit the public good. "Pro forma" describes something done as a formality, typically for compliance or procedural reasons without substantial value or effect. "Post hac" translates to "after this," generally used to indicate a cause-and-effect relationship in time, such as in the phrase "post hoc reasoning," which suggests one event causes another simply because it follows it.