It means that the two parties involved in the trade know what is being traded, so that each can decide whether or not they think it is a fair deal.
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The use of money increases economic efficiency because without it, we would be a barter system. In a barter system, if I want potatoes, and have oranges to trade, the person with the potatoes has to want oranges to be willing to trade with me. With the use of money, I can give him a known amount of value in money, which he can buy what he wants to with.
West Africa. They would trade Africans for their poisoners of war. There prisoners are often Africans. Well mostly. But from their they would go to the islands to sell them for money. Then go to Britain to give them the money and get more goods to trade.
All countries are trying to become uniform in weights and measurements etc. There would be no more conversions necessary making trade easier for all.
Before money existed - and even today! - people trade something that they have or something they can do for something someone else has or can do. It's called the barter system.
You would get money from the trade-in, then you may have enough for a PSP
they did not actually have money they would trade
the would trade
It depends on what games they are and where you trade them in.
You would use a measuring tape, with measurements in centimetres.
Without money the world would have been dominated by barter trade
Really only trade would be a money substitute. That is it. But money substitutes are things that can be used in place of money.