I'm afraid I don't know all that much about it, having never used it personally. But I've got to get my two cents in here anyway ;).
StackOverflow
^ This is a pretty good explanation. As I understand it, it has to do with sending a serializable object through streams or over the network. I think it has something to do with persistence too but I'm not sure. Chances are, if you're not doing either of those things, you can just ignore it and add an annotation to suppress the warning.