The Gravestone Doji is a single day pattern. This occurs when the open and close are at the bottom. Candlestick has a long upper shadow and no lower shadow.. It is OK for Gravestone Doji  to have a very small lower shadow. 

Gravestone Doji is considered as a possible top reversal pattern i.e bearish.

Psychology of Gravestone Doji pattern is that the market is on an uptrend and on the day when Gravestone Doji appears bulls  are able to push prices upwards. During the day, bears take over control and push prices back to the start of the day price. It is very common for the upper  shadow of the Gravestone  Doji to act as an area of support for future prices. 

Gravestone Doji is the opposite of Dragonfly Doji.

The longer the upper shadow and higher the price level of the Gravestone doji indicates strong bearishness.