A coin is normally a round piece of metal that is used as currency, or money. Coins have been made for about 2600 years; the first place to make coins was Lydia (modern Turkey). These coins were made of Precious metals and allowed people to trade with a standard amount of metal.
The different decorations on each side of a coin might be used to decide things randomly. This is called "tossing a coin". A person can throw the coin into the air and catch it. You then look at which side is facing up. If the head is facing up it is called "heads", if the other side is facing up it is called "tails". Before tossing the coin someone has to decide what each side means. Tossing a coin can be a type of gambling, which is illegal (against the law) in some countries.
Some people see coins as a sign of greed, such as some Communists and Puritans, who sometimes condemn over-hoarding of coins, and ascetics, who often keep little in the ways of money (coins), leading a "poor"-lifestyle.
Because coins have been made for a very long time, some people collect old coins. They can be much cheaper than other old things, especially if they are made of cheap metals like copper. Older coins normally cost more than newer ones, but rarity matters more-some coins from the 1920s cost vast sums, while some Roman coins cost very little.