What is open?

The term open has a couple of different meanings for example the most common usage is the opening time of the exchange office. As we all know it NYSE and Nasdaq opens at 9:30 am EST, and the AMEX opens at 9:00am EST. Also the term open is used on those orders which weren’t executed yet but they are still valid, these orders stay open until they expired or they are executed. Also not so common but is used on establishing an account or a letter of credit. And it’s also used as open or opening when the first price is set of a stock or share when the trading session begins.