Glossary
Order block OB
In short
An order block is the last opposite candle before a strong move that breaks structure. Traders watch it as a zone where price may react when it returns.
Bullish and bearish
A bullish order block is the last down candle before a strong move up. A bearish order block is the last up candle before a strong move down. The zone runs from the high to the low of that candle, often with a line at 50%.
Used once
Once price has traded back into an order block, it counts as used (mitigated). Many traders give a fresh block more attention than one that has already been tested.
Not every block matters
Blocks that led to a real break of structure, and blocks in discount for longs or in premium for shorts, are the ones traders filter for.