What is the "exclusionary rule" in criminal law?

The exclusionary rule is a key principle in criminal law that prohibits the use of evidence obtained in violation of a defendant's constitutional rights. Specifically, it aims to deter law enforcement from engaging in unlawful practices, such as searches and seizures that do not comply with the Fourth Amendment. When evidence is obtained improperly—say, through an illegal search without a warrant or probable cause—it cannot be presented in court against the defendant.

This rule is foundational because it upholds the integrity of the judicial process by ensuring that convictions are based on properly obtained evidence. If the exclusionary rule were not in place, it would undermine the rights of individuals and could lead to issues of police misconduct and violations of constitutional protections.

The other options focus on different legal principles or practices that do not relate to the exclusionary rule's core function of regulating the admissibility of evidence based on how it was obtained. Therefore, the correct definition of the exclusionary rule highlights its role in maintaining lawful evidence standards in criminal proceedings.