A chlorofluorocarbon is a human-made chemical that contains chlorine, fluorine, and carbon. People almost always say CFC, which is much easier, and this entry is that chemical — not some other thing those three letters might stand for. For years CFCs were used in fridges, air-conditioners, spray cans, and foam, because they were stable and did not catch fire easily. Then scientists showed they rise high in the sky and eat away at the ozone layer, the shield that blocks a lot of the sun’s harsh rays. Most countries agreed to stop making the worst CFCs. Though actually, people mix this story up with climate change. The famous CFC crime is the ozone hole. CFCs also trap heat, but the everyday warming word is more often carbon dioxide, which is a different chemical. Some replacements spare ozone and still trap heat. Older speakers may still say Freon, which began as a brand name.