A magnet is a piece of metal with a strong attraction to another metal object. The attraction a magnet produces is called a "magnetic field."
You might cover the front of your refrigerator with magnets, which stick to its metal surface. Other kinds of magnets are even more powerful, strong enough to pick up entire cars, for example. Most magnets are made of iron or an iron alloy, and magnets are at the heart of many common items like cassette tapes, credit cards, toys, and compasses.