A coin has its own blockchain. There is no difference between a coin and a cryptocurrency. Examples are Bitcoin, Ethereum Coin.
A Token is hosted on another currency’s blockchain. Example: FirstBlood Token.
“Currency is a generally accepted form of money, including coins and paper notes , which is issued by a government and circulated within an economy.”
What is more, the currency must have value in the market.
Basically, cryptocurrency is not that different from tokens. Once tokens are issued by some enthusiastic developers group and someone bought it (or received for some job) and can trade them, it becomes cryptocurrency.
However, tokens can be much more than cryptocurrency. They can be used for various cases in the smart contracts ecosystem which accepts that token. For example, Basic Attention Tokens will be used as token to use its advertising service. This means, that BAT tokens value will potentially increase as all people will have to buy it to use the service.
So to conclude, crypto currencies just help transfer value in accepted way (as physical money), as tokens can be used for various use cases in blockchain.