A creditor's claim against property to secure payment of a debt or performance of an obligation (§ 101(37), Bankruptcy Code). Liens may arise voluntarily, such as a mortgage on real property, or involuntarily by operation of law, such as a judgment lien or tax lien. Liens may be perfected or unperfected. A perfected lien gives a creditor a priority interest in the encumbered property against third-party creditors, and is generally obtained by taking steps under state law that give third-party creditors notice of the lien.