The opening range is the high and low established during the first minutes of a trading session — commonly the first 5, 15, 30, or 60 minutes — used as reference levels for the rest of the day. The session open concentrates overnight orders and fresh information, so the early range often frames the day’s battlefield.
The classic application is the opening range breakout (ORB): buy a break above the range high or sell a break below the range low, with a stop inside the range, on the thesis that an early escape from the opening auction tends to extend. The mirror application fades failed breaks back into the range, treating them as sweeps of early liquidity.
The opening range is fully mechanical — anchor time, duration, and breakout rule are exact numbers — which makes it one of the easiest day-trading concepts to backtest honestly, and one where results depend heavily on the market, session, and costs assumed.