What does Chance of Rain mean?

I'm contemplating camping this weekend, and with 3 of my children at 3 years and younger I'm a little concerned about the forecast of 60% of rain for Saturday.

I've always wondered what Chance of Rain means. Does it mean there will be that much rain over the entire area over the course of a day? Or Chance for any given moment of a day there will be rain in one area? Or chance that rain will develop over all or part of the viewing area? I've always wondered at a time when I'm away from the computer -- but today I'll check Google.

From Carl Bialik's blog, it looks like different meteorologists define chance of precipitation differently. Some give the worst case scenario, but all use the term inconsistently. At least I've been confused for a reason. For What It's Worth paraphrases Weather For Dummies.

In conclusion, I can't conclude anything. However, I've decided what I really care about for camping is expected duration of rain for the area -- a storm or two is fine, but a day cooped up in a tent with my one and a half year old would wear on both our nerves.