WRT Halo 3: Got a call from Gamestop

[Taso]

So I "reserved" a copy of the game, gave them some amount of money, and they called me last night or two nights ago and said I had to be there Monday night at 9:00pm, and wait for the 12:00am midnight release to be sure I get a copy of the game.

I don't understand, maybe I don't know the word well enough, but doesn't "reserve" mean they hold it for me (and anyone else who reserved a copy) until I come in and pay the rest that I owe? Isn't that generally how things work, isn't that the POINT of reserving something?