The constitutionality of something refers to whether or not it is in line with the principles and provisions outlined in the Constitution. In the context of a legal issue, it means determining if a law or action is allowed under the Constitution.
Related terms
Judicial Review: Judicial review is when the courts have the power to determine if laws or actions are constitutional.
Due Process: Due process refers to fair treatment and protection of individual rights under the law.
Separation of Powers: The separation of powers refers to how governmental powers are divided among different branches (legislative, executive, judicial) to prevent any one branch from becoming too powerful.