Final answer:
When a judge uses the decisions of earlier cases to inform their ruling on a current case, they are relying on precedent, a principle underpinned by stare decisis, meaning "to stand by things decided".
Step-by-step explanation:
Relying on Precedents and Stare Decisis in Law
When a judge looks to the decisions of previous cases when deciding a current case of a similar nature, the judge is said to be relying on precedent (option A). This is a practice rooted in the principle of stare decisis (option B), which literally means "to stand by things decided" in Latin. Habeas corpus and a writ of certiorari are unrelated to this practice and thus are not the correct answers for this question.
Stare decisis is a fundamental legal doctrine that ensures stability and predictability in the law by requiring that later courts follow the legal determinations made by previous courts in similar cases. However, it does not eliminate the possibility of the law evolving, as precedents can and do get overturned when circumstances or interpretations change, which has been evident in cases such as Brown v. Board of Education, which overturned Plessy v. Ferguson.
Overall, precedent is crucial for the ongoing operation of courts, guiding the direction of the legal system and providing a framework within which judges must operate unless there is a strong justification for deviation.