The two most common types of debt are secured and unsecured. Secured debt is typically backed by collateral (an asset that possesses value). The lender has a lien on the collateral (they can take the asset) as an assurance of some repayment should you fail to make payments. For example, if you purchase a car, the lender will have a lien on the car and could repossess it if you fail to make your payments per the terms in your loan agreement.
An unsecured debt is a debt is not backed by collateral. The lender has no assurances, other than your income and credit history that you will repay what you borrowed in full and on time. Credit cards are examples of unsecured debt. If you fail to make your payments, your account can be turned over to a collection agency and your credit report will reflect the negative activity most likely resulting in a lower credit score.