Copper is a reddish-brown metal that humans have used for thousands of years. If you've ever seen a penny (which is coated with copper), you know its distinctive warm color. Copper is special because it conducts electricity extremely well, which is why the wires inside your walls that carry electricity throughout your house are made of copper. It also conducts heat efficiently, making it perfect for cooking pots and pans.

Ancient people discovered copper around 10,000 years ago, making it one of the first metals humans learned to work with. When ancient craftspeople mixed copper with tin, they created bronze, a harder metal that was so important it gave its name to an entire era: the Bronze Age. Copper also forms a blue-green coating called patina when exposed to air and moisture over time. The Statue of Liberty's famous green color comes from this natural process.

The word can also mean a police officer, though this is an informal and somewhat old-fashioned usage. People might say “the coppers are coming” in an old detective story.