When someone’s heart has stopped and they have stopped breathing, other people may press again and again on the chest, and sometimes also blow air into the mouth, to try to get the heart and the breathing started. That whole action is CPR. The letters stand for a long hospital name, cardiopulmonary resuscitation, but almost nobody says the long name in ordinary talk — they say do CPR or give someone CPR. You hear it in first-aid class, in hospitals, and in films when someone collapses. Though actually, many classes now teach that for people who are not doctors, calling for help and pushing on the chest matter most, and breathing into the mouth is not always the first thing they ask you to do. The word itself still covers both the pressing and the breathing. It is a serious word, not a joke, and it is the everyday name, not a slang one.