Reputation is from going on a [[Village deeds|deeds]] of your own kingdom and doing something against the [[Village deeds|deed]]s law.
If you are a Whitelighter and your rep goes below -100200, you will automatically become a Blacklighter.
If you die with less then 0 rep, you will lose 5x normal skill loss ( 1.25 skill if you die with less then 0 rep)