OK, I think I understand. It sounds like something used around here that's called the extra batter (EB) rule. Some summer leagues for the younger kids use it.
Essentially it states that a team may bat as many players as they wish. The catch is that if you start the game batting, for example, 12 players you must maintain 12 batting positions for the entire game. If you have 12 players and they all bat there is a possible problem. If you lose a player through ejection, injury or illness you have to take an out each time that batting position comes up. This is to prevent teams from skipping batters by saying that they have decided not to use an extra batter later in the game.
You can substitute for an extra batter if you have more players than batting positions. And generally, these leagues allow re-entry so moving kids in and out of the lineup isn't a problem.