What does charge off on a credit report mean?

It means the creditor has essentially given up on trying to collect a debt from you (though they may have sold it to a collection agency for pennies on the dollar). There's also a "paid charge off", which means that, after they gave up, you paid it off anyway, which really doesn't do you much good, because a paid charge off looks just as bad on your credit report as a charge off. A charge off, of either kind, is the third worst thing you can have on your credit report, after (1) bankruptcy, and (2) repossession/foreclosure.