means An official decision or judgment, especially one handed down by a judge, court, or authority that settles a question or sets a binding standard.

from From the verb 'rule,' which traces back through Old French 'reuler' to Latin 'regula,' meaning a straight stick, bar, or measuring rod — the same root behind 'regular' and 'regulate.' That literal ruler for drawing straight lines became a metaphor for the lines we must walk: a rule is the standard you measure conduct against, and a 'ruling' is the moment someone draws that line for everyone.