The Bullish Engulfing Pattern typically appears at the end of a downtrend. The market drops, and a down candle forms. Next, a candle appears with a real body that wraps (or engulfs) the body of the previous session's down candle.
If the market is strong, the lows of this pattern should act as support. So, if buying into a Bullish Engulfing Pattern, you should place a technical stop just under the lows of this pattern.