A more thorough explanation:

Judicial review is a concept in the US government system that allows the judiciary to review and possibly invalidate actions taken by the executive and legislative branches of government. This ensures that these branches abide by the constitution. The power of judicial review is not explicitly stated in the Constitution but is an implied power derived from Article III and Article VI.

In the landmark case of Marbury v. Madison, the Supreme Court used judicial review to strike down an act of Congress as unconstitutional. Chief Justice John Marshall famously stated, "It is emphatically the duty of the Judicial Department to say what the law is. Those who apply the rule to particular cases must, of necessity, expound and interpret the rule. If two laws conflict with each other, the Court must decide on the operation of each."

Another example of judicial review is when the Supreme Court declared segregation in public schools unconstitutional in the case of Brown v. Board of Education. This decision overturned the "separate but equal" doctrine established in Plessy v. Ferguson.

These examples illustrate how judicial review allows the Supreme Court to interpret the Constitution and ensure that the actions of the other branches of government are in line with it.