Debtor:
One who owes something and makes payments to a creditor.
 

Default:
The omission or failure to perform or fulfill a legal duty, obligation, or promise (i.e. to pay a debt).
 

Due diligence:
Exhaustive research on a transaction, income stream, client, and/or payor. Due diligence may involve credit checks, appraisals, UCC searches, lien searches, or on-site visits with clients.