The term "Trading day" is used to refer to a day on which a particular exchange is open. U.S. Stock exchanges, for example, are open on Mondays through Fridays. There are no trading days (The U.S. Stock Exchanges are closed) on weekends and on some holiday days (New Year's Day, Good Friday, Memorial Day, Independence Day, Christmas Day...).
For example, on each trading day, the regular trading hours on the NASDAQ starts at 9:30 a.m. and ends at 4:00 p.m. ET. The New York Stock Exchange is also open from 9:30 a.m. to 4:00 p.m. ET.
On some particular days, the trading day is shortened. For example, on the day after Thanksgiving, which is a Friday, U.S. markets closes at 1:00 p.m. ET.
There are also no trading days, for the U.S. Stock Markets, on some particular non-holiday days. Example, the market is closed on a Monday if a stock market holiday occurs on the previous day (Sunday).
