The bullish engulfing pattern is a two-candle reversal pattern. The second candle completely ‘engulfs’ the real body of the first one, without regard to the length of the tail shadows.
This pattern appears in a downtrend and is a combination of one red candle followed by a larger green candle. On the second day of the pattern, the price opens lower than the previous low, yet buying pressure pushes the price up to a higher level than the previous high, culminating in an obvious win for the buyers.