Counterintelligence is the work a country does to stop other countries — or enemy groups — from stealing its secrets. Intelligence here means secret information and the people who hunt for it, not “being clever.” So counterintelligence is the shield: catching spies, feeding them false stories, watching who is asking too many questions, protecting codes and plans. You hear it in government, military, and spy stories. It is formal. Though actually, films make it look like one genius in a dark room; in real life it is slow checking, rules, and a lot of paper. It is close to counterespionage, but counterintelligence is the broader office word for defending your secrets.