Open
What it is:
In the stock markets, open refers to the beginning of the trading day or the price of a security at the beginning of the trading day.
How it works (Example):
The New York Stock Exchange has the most famous opening bell. At 9:30 am Eastern time, it rings. At that time, the last trading price for each security on the exchange the day before (the closing price) becomes the opening price, or the open.
Why it Matters:
The open is the start of a new day, though it is important to note that that doesn't necessarily mean trading hasn't been going on right before the open. After-hours markets remain open as do other exchanges in other countries and time zones, which provides opportunity for the price to change right up until the open in many cases.
