What is "bright-line rule"

n. 1 (context idiomatic English) A clear-cut, easy to make decision 2 (context legal English) A clearly defined rule or standard, comprised of objective factors, which leaves little or no room for varying interpretation.

A bright-line rule (or bright-line test) is a clearly defined rule or standard, composed of objective factors, which leaves little or no room for varying interpretation. The purpose of a bright-line rule is to produce predictable and consistent results in its application. The term "bright-line" in this sense generally occurs in a legal context.

Bright-line rules are usually standards established by courts in legal precedent or by legislatures in statutory provisions. The United States Supreme Court often contrasts bright-line rules with their opposite: balancing tests (or "fine line testing"), where a result depends on weighing several factors—which could lead to inconsistent application of law or reduce objectivity.