It obviously has your name, match results and a calculated level and it has that for everyone on the system for every match they've played. We may also have your date of birth if that has been sent to us either via results or as an import from your federation and that is stored encrypted and as a write-only field. I.e. not even you or admins can see your date of birth - it is only used to generate your age group.
We are also likely to have some sort of federation membership ID that has come over with your results. That is normally only visible to you (if the system is in the correct federation mode) or admins.
If you register as a member then we also ask for an email address and for you to identify which player on the system you are. That's it. Your password is encrypted before it's put into the database so we have no idea what it is. We also don't send emails out unless we have a query specifically related to you.