Opening Price
The price at which a security first trades upon the opening of an exchange on a given trading day.
Investopedia Commentary
Quite commonly, a security's opening price will not be identical to its closing price. This is due to after-hours trading and to changes in investor valuations or expectations of the security occurring outside of trading hours. The opening price of a security serves as a benchmark for the day: if the security finishes trading at a higher price it is said to have closed up, and if it finishes trading below the opening price it is said to have closed down.
Related Links
The Nitty-Gritty Of Executing A Trade
Getting to Know Stock Exchanges
The Tale Of Two Exchanges: NYSE And Nasdaq
See also: After Hours Trading - AHT, After The Bell, At-The-Close Order, At-The-Opening-Order, Close, Closing Bell, Open, Opening Bell, Wide Open