Why is there a Zero in the Planning Poker deck?

It's there for whatever you want it to be. We just changed something on Mountain Goat today where my programmer had accidentally labeled a field "Your Name" when I wanted it to be "First Name". It as causing emails to go out as "Dear Jane Doe," instead of a more friendly "Dear Jane,". Technically he just fixed it on the spot but I could have put it in our product backlog and had it estimated as a '0' to be done later. We often have a few zero-point stories hanging around for a short time.