Answer:
If something is fungible it can be broken into pieces without losing much of its value. Something is fungible or it is not. Gold can be melted down and split into smaller bars with no loss of value, therefor it is fungible. Gasoline is fungible, you can sell two half gallons for the same price as a single gallon. A race horse is not fungible. An iPod is not fungible. A rare coin is not fungible. You're not fungible.
Hope this helps.