A marubozu is a candle with little or no wick — the body fills the whole range. The open is the high (or low) and the close is the low (or high), meaning one side controlled price from the first tick to the last. It is the purest single-candle picture of conviction.
Bullish and bearish
A bullish marubozu opens at its low and closes at its high — relentless buying with no pullback. A bearish marubozu opens at its high and closes at its low — relentless selling. Either one often kicks off or extends a strong move, because the lack of a wick means the controlling side never gave ground.
How to use it
A marubozu breaking out of a level is a strong confirmation that the break has force behind it. The candle's range also gives a practical stop: a move back through the entire marubozu body negates the conviction it showed. Beware the climactic marubozu after a long run, which can mark exhaustion rather than continuation.