A trading session is the active period during which an asset or instrument is available for buying and selling. Trading sessions generally correspond with market predefined opening and closing times, establishing a prescribed period of activity during which specific trading instruments can be traded. The hours of a trading session vastly depend on the asset or market being traded.

In the United States, the equity market opens daily at 9:30 a.m. Eastern Time (ET) and closes at 4:00 p.m. ET (although a closing auction can start at 4:00 p.m. ET). This standard trading session has become known as the "NYSE Core Trading Session," and it marks the most active period for equity trades within a 24-hour time frame. During this core session, the trading volume is highest and news stories that could affect the underlying prices of securities are commonly released.

Around the world, different markets may have varying trading sessions. For example, the forex market may be open during overlapping periods in different world time zones, due primarily to globalization and the ability to access foreign exchanges electronically. Global exchanges enable investors in different regions to trade different assets 24 hours a day, five days a week (i.e., Monday through Friday).

In addition to the standard core asset trading session, there are “pre-market” and “post-market” sessions. Pre-market trading begins at 8:00 a.m. ET and lasts until the core market open of 9:30 a.m. ET. The post-market trading window starts after 4:00 p.m. ET and typically closes at 8:00 p.m. ET. While liquidity is usually quite low, these extended hours provide the opportunity to trade around news events and business releases that may take place when the primary session is closed.

Overall, a trading session is the official active period in which a given asset or instrument can be traded by market participants. It is critical for traders to be aware of the begin times and end times for any sessions in which they plan to trade. An understanding of the trading sessions for all major asset classes can help traders to plan appropriately and develop strategies that fit their trading style and objectives.