A long black day is followed by a white day that gaps below the black day’s
low and closes within and above the midpoint of the black day’s body.
In a downtrend or during a pullback within an uptrend, the stock gaps
down, finds some buyers and then rallies. This simply signifies the possibility
of a reversal that is more reliable if the gap down occurs at support
and the white day is accompanied by a surge in volume.
The bullish Piercing Line is similar to bearish On Neck, bearish In Neck,
bearish Thrusting, bullish Engulfing, and bullish Meeting Lines.