The term commonly used price in exchange activities. To say something of goods used in the unit price of money. Thus, understanding the value of a good price is expressed in units of money. Not every item has a price, only economic goods because the price alone that have acquired it requires a sacrifice that led to the offering is the factor of scarcity or infrequency. So the stuff has a price because the goods on the one hand and on the other useful stuff is limited or scarce. In accordance with its terms, is called simply a balance because the price will be a balance between the quantity of goods demanded (purchased) with the goods offered (sold). Only the balance is due to the interaction between buyer and seller to make a request to hold offerings in the market.