The final price at which a security is traded on a given trading day. The closing price represents the most up-to-date valuation of a security until trading commences again on the next trading day.
Taobiz explains Closing Price
Most financial instruments are traded after hours , so the closing price of a security may not match its after-hours price. Still, closing prices provide a useful marker for investors to assess changes in stock prices over time - the closing price of one day can be compared to the previous closing price in order to measure market sentiment for a given security over a trading day.