This is the number of participants in the tournament.
Note: For a single game is the number of participants = 2.
The declaration "3 of 5" means that the tournament is for 5 Players and 3 Players are already registered.
The choice of the number of participants is limited by the chosen form of play:
This can take two or more players. The matches of the tournament all start simultaneously. For more than two players, only odd numbers of participants are allowed, so that each player has equal number of times white or black.
Quick chess tournaments are only for 2 players, since you should play only one quick chess game simultaniously.