A trading session refers to a specific period during which financial markets are open for buying and selling assets. It typically lasts for several hours, with different exchanges or countries having their own schedules. For example, in the United States, there are three main stock market sessions - the pre-market session (4:00 AM to 9:30 AM), the regular trading session (9:30 AM to 4:00 PM) and the after-hours session (4:00 PM to 8:00 PM). During these periods, investors can buy or sell stocks through their brokers. The term "trading session" is also used in reference to other financial markets such as foreign exchange, commodities, and cryptocurrencies.