currency
In French, 'monnaie' is used to refer to the system of money in general use in a particular country. It is also commonly used in situations where you would refer to change, as in small denominations of money. For example, 'Avez-vous de la petite monnaie?' means 'Do you have small change?'
Where is my change?
This is a question someone might ask after paying for something to know where their change is, if they were expecting some.
This coin is very old.
This phrase is used to describe a coin (a form of currency) that has been around for a very long time.
How much change do you have?
This phrase is likely to be used in a situation where someone is asking another person how much change or coins they have, probably because they need some.