ORB is an acronym for the
Opening Range Breakout, a trading strategy devised by Toby Crabel. [see also Opening Range]
Using this strategy, the trader places a buy stop just above the Open price plus the Stretch and a sell stop just below the Open price minus the Stretch. The first stop triggered enters the trader into the trade and the other stop becomes the protective stop.
Crabel's research shows that the earlier in the trading session the entry stop is hit the more likely the trade will be profitable at the close. A market movement that kicks off a trend quickly in the current trading session could add significant profit to a trader's position by the close and should be considered for a multi-day trade.
Extending Crabel's research results it is obvious that as time passes and we are not filled early on then the risk increases and it becomes prudent to reduce the size of the position during the day. Trades filled towards the end of the day carry the most risk and the later in the day the trade is filled the less likely the trader will want to carry that trade
overnight.
Variations of this strategy include the Opening Range Breakout Preference (ORBP).
Source:
https://www.mypivots.com/dictionary/definition/150/opening-range-breakout-orb