A lien is a legal claim or right against a property that ensures payment of a debt or obligation. When a lien is placed on a property, the owner cannot sell or transfer the property without first settling the debt. Common types of liens include mortgages, tax liens, and mechanic's liens. Liens can be voluntary or involuntary. A voluntary lien is created when a property owner agrees to it, such as when taking out a loan to buy a home. An involuntary lien, on the other hand, is imposed by law, often due to unpaid debts or taxes.