What do restaurants mean by "All You Can Eat"?

What it means seems obvious but I guess not everyone finds it obvious. Does it mean that you can start eating at opening time, keep eating till closing time, and if you’re still not full come back the next day? Someone is suing the restaurant, by claiming: “It says all you can eat and I can eat more and more and more, I’m not full yet.”*
http://tinyurl.com/j2r3hxh See the second and 3rd and the 3rd from the bottom results.
I’m giving the search result link because I don’t know these sites.