Trading positions not closed by the end of the trading day and held overnight. For securities trading, overnight positions expose the investor to risk because a number of events can negatively impact a position while the trading floor is closed. 
 
|||In forex trades, 5pm EST is considered the end of the trading day. Positions opened at 4:59pm EST and closed at 5:01pm EST are considered overnight positions because a new "day" begins after 5pm. Rollover interest is paid out or received on overnight positions based on the closing interest rate.