Order block
The candle an impulse started from — where a position was built.
An order block is the last candle before a strong move, usually opposite to it in direction. The logic is simple: to push price, someone had to build a position first, and this is where they did it. So when price returns to that zone it often reacts — the same participant's interest is still there. Order blocks are frequently confused with imbalances: an imbalance is a gap inside the impulse, an order block is the candle the impulse began from. Side by side they reinforce each other.