it means its disposable-you cant refill the film. So you get like 28 pictures-once that roll is done- you cant go buy another and stick it in the camera and keep using it.
You can use it under water the entire time/fore all 28 exposures-they turn out pretty well for a disposable camera too.
Check the end tabs of the box, I think that they are stamped into the cardboard, but I am not sure. My grandchildren used the ones that I purchased while on a family vacation this past summer, so I don't have the boxes to check. If you keep the camera from freezing or baking in the sun (like in a hot, parked car) I think that it wouldbe fine for a year or two. Sorry that I couldn't be more specific.