exclusionary rule

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The rule, based upon the Fourth Amendment to the US Constitution, that prevents the use of illegally seized evidence against a defendant in a criminal trial.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun US, law A doctrine which requires that evidence obtained as the result of an illegal act on the part of law enforcement personnel (such as a warrantless search, or continued questioning a witness who has invoked the right of counsel) must therefore be excluded from being admitted as evidence in a trial.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a rule that provides that otherwise admissible evidence cannot be used in a criminal trial if it was the result of illegal police conduct