What is Copper ?
Copper is (noun) 1. a reddish metal which turns green when exposed to air Copper is a good conductor of electricity. The end of the copper wire should be attached to the terminal. 2. a policeman Watch out! there’s a copper coming. 3. a small coin made of copper or other brown metal It only costs a few coppers. The beggar was asking for any spare coppers.
source: Easier English, Student Dictionary Upper Intermediate Level