Suppression occurs when evidence collected in violation of the Constitution becomes inadmissible at trial. Evidence excluded this way is referred to as being “suppressed.” This is known as the Exclusionary Rule.
The process for suppressing evidence involves filing a "motion to suppress". For instance, if a defendant confesses to murder while under arrest but was not read their Miranda rights, the defendant's attorney should file a motion to suppress in order to bar the confession from being used as evidence at trial.
Another common ground for suppression is unlawful search and seizure by the government (meaning without a proper warrant or probable cause) in violation of the Fourth Amendment.
See also: fruit of the poisonous tree
[Last updated in June of 2024 by the Wex Definitions Team]