A creditor is a person, institution or business to whom money is owed. Secured creditors are creditors who have taken some measure to protect themselves and hold a mortgage, pledge, lien or similar instrument on, or against, your property. If they are not paid, they can enforce their claims by recovering the assets on which they hold security.
Unsecured creditors are creditors who do not have any security for the debt owed to them.
A preferred creditor has a priority claim to funds in the bankruptcy estate.