The Gravestone Doji is a candlestick pattern in which the opening and closing price are equal for the time period in question, and at the same time, both open and close prices occur at the low of the day. So in essence, open price = close price = low price.
The Gravestone Doji is more commonly a bearish reversal pattern, even though bullish reversals have been known to occur when this pattern appears at the end of a downtrend (rare). The Gravestone Doji is a bearish reversal pattern when it occurs at the end of an uptrend, suggesting that buying pressure is exhausted and sellers have pushed prices of the asset from the high back to the open price, and leave it there to close the time period, preparing to continue selling.
The Gravestone Doji is more accurate when it is used as a bearish reversal pattern.