It's a flexible seat package. I don't know the exact details so I'm going to make them up, but something like this:
Let's say we have 17 home games, you get 17 "passes". The week before each game you could opt-in to each game, and thus you'd get one ticket to every game (where you sit depends on the game.)
Or, you could choose not to attend a couple games, you could use multiple passes for the same game. Say you don't think you can make midweek games, so you're going to use more passes on the weekend games to bring friends/kids/whatever. However you want to do it.
They have a similar thing for football. I think it's a good idea for people who can't commit to every game but want to make sure they have a few tickets for some games.