A period of time consisting of one day of business in a financial market, from the opening bell to the closing bell. Within the time frame of the trading session, all orders for the day must be placed, and buyers and sellers both participate in setting current market prices. Taobiz explains Trading Session The investor's concept of the trading session has broadened in the past decade as after-hours markets, ECN exchanges and other technologies have entered the marketplace. This increased access to the markets and information can overwhelm an individual investor with news, but long-term investors know that tuning out the day-to-day noise of the stock market is a key element of success.