A Gravestone Doji candlestick forms when a financial asset opens, trades significantly higher during the trading session, but then closes at or near the same level as the opening price. This results in a candle with a long upper wick (or shadow), a very small or non-existent lower wick, and no real body because the open and close prices are nearly identical.

The name "Gravestone" comes from its appearance, which resembles a gravestone, symbolizing a potential reversal in the current trend. It often occurs at the top of an uptrend and signals a bearish reversal.

The formation of a Gravestone Doji suggests that buyers initially pushed the price higher, but sellers took control later in the session, driving the price back down to the opening level. This indicates that buying pressure is weakening, and a potential reversal to the downside might occur. However, traders typically wait for confirmation from the following candles before making decisions, as Gravestone Dojis alone don't guarantee a reversal.

In summary, a Gravestone Doji is a significant warning sign of potential trend exhaustion, particularly in bullish markets, and is most reliable when seen in conjunction with other technical indicators.