When a debt collector or collection agency contacts to recover past-dues, debts from creditors, or credit card payment. All this procedure is called debt collection. If you haven't made loan or credit card payments or any other dues of any company and they are severely past due, then a debt collection agency can contact you.
A US base agency Cedars Business Services specialize in debt collections, they have a professional team and know the tricks of the trade. So companies will pay debt collection agencies a portion of what they collect.