Games with long time limits, such as the best-of-seven Meijin and Kisei, take 2 days to play 1 game. At the end of day 1, the next move is written on paper and put in an envelope. That's the "sealed move."
POINT 01
The last move of day 1 is written on paper and sealed.
As the end of day 1 approaches, the player to move writes the next move on a sheet instead of playing it. The sheet is sealed in an envelope, and the referee keeps it until the next morning.
On the morning of day 2, the referee opens the envelope, reads the move aloud and places the stone on the board, and the game resumes.
- The player to move at that point seals the move
- Time spent deciding the sealed move comes out of the time limit
- Day 2 begins with opening the sealed move
POINT 02
To remove the unfairness of "getting a whole night to think."
If day 1 simply ended with a move on the board, the opponent could see it and spend the whole night thinking about the reply. With a sealed move, both players spend the night without knowing the other's move, which keeps things fair.
So choosing when to seal is part of the strategy too. Sometimes an obvious move is sealed, and sometimes a player deliberately seals in a difficult position.
POINT 03
On the night of day 1, enjoy guessing the sealed move.
At the end of day 1, broadcasts and commentary often discuss "where is the sealed move?" List a few candidates and check your answer when it is opened the next morning. It's a way of enjoying that only 2-day title matches offer.