Coins
Coins are legal tender and to be considered a coin it needs to meet certain criteria such as:
 It needs to be struck by a government mint.
 It needs to be assigned a specific monetary value.
 It needs to be intended to be used in circulation as money.
Although coins have an assigned value, many surpass this original amount, especially if they are rare or made with precious metals.

Medals
Medals, on the other hand, are typically used to commemorate a certain person or event, and they are not intended to be used as legal tender. Medals or tokens are typically traded amongst coin collectors or sold because of the value of the materials they were made from.
Medals or medallions, look like coins, but they do not act like coins in that they are not:
 Struck (the term used to mean manufacture of a coin) or minted by a government
 Given a monetary value by a government
 Intended to circulate as money
Medals or medallions are usually struck as a memento of a person or event, in order to remember their importance in history, but are never intended to be used to buy a loaf of bread or a shirt.
Here is a further distinction: coins that are struck for monetary use by an organization other than a government are not considered coins, but tokens.