Entrapment is a legal term that describes what happens when someone is tricked into committing a crime. Police officers have to be careful not to use techniques that might be seen as entrapment.
A defense attorney might try to prove that her client was a victim of entrapment in order to get charges dropped or to influence a jury to find the defendant not guilty. Legally, entrapment is considered unfair because it influences someone (who otherwise wouldn't) to break the law. The word's been around since the 16th century, meaning "being caught in a trap," but the legal definition arose toward the end of the 19th century.