A more thorough explanation:

The Rule of Four is a convention that requires at least four justices of the U.S. Supreme Court to vote in favor of granting certiorari for a case to be heard by the Court.

Certiorari is an extraordinary writ issued by an appellate court, at its discretion, directing a lower court to deliver the record in the case for review. It is a way for a higher court to review the decision of a lower court.

For example, if a person is convicted of a crime and appeals the decision to a higher court, the higher court may issue a writ of certiorari to review the lower court's decision.

The U.S. Supreme Court uses certiorari to review most of the cases that it decides to hear. The Court has the power to define its own institutional role through its control over the cases that come before it.

One example of the Rule of Four in action is when a case called Obergefell v. Hodges was heard by the U.S. Supreme Court in 2015. This case dealt with the issue of same-sex marriage and whether it was constitutional. Four justices voted in favor of granting certiorari, and the case was heard by the Court.

Another example is when a case called Texas v. Pennsylvania was brought before the Court in 2020. This case dealt with the 2020 U.S. Presidential Election and whether certain states had violated the Constitution in their handling of the election. Four justices voted against granting certiorari, and the case was not heard by the Court.

These examples illustrate how the Rule of Four determines whether a case will be heard by the U.S. Supreme Court. If at least four justices vote in favor of granting certiorari, the case will be heard. If not, the case will not be heard.