What does a market demand curve predict?

I believe economists create demand curve to predict how people will change their buying habits when prices change. A demand curve is plot of Quantity of products or services demanded in the market against the prices for a given period of time. The price appears on the horizontal axis and the quantity demanded on the y axis. The demand is the quantity of goods or services that the consumers are willing and able to buy at a given period of time.  

Explanation:

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