Answer:
Double coincidence of wants - a situation where two individuals each want some good or service that the other can provide
Double coincidence of wants occurs when in a transaction between two or more individuals, each want to obtain the good or service that the other is offering.
Barter - trading one good for another without the use of money
In barter, people trade a good or service for another good or service, without the use of money as medium of exchange. An example of barter is trading a cow for a sheep.
Money - whatever serves society in three functions: medium of exchange, store of value, and unit of account
Money is any good that serves the three purposes of money, store of value to serve as a medium to save or to accumulate wealth, medium of exchange to trade goods and services, and unit of account to measure the value of goods and services under a common guide.