What is Tax Lien?

Legal Definition
A tax lien is a lien imposed by law upon a property to secure the payment of taxes. A tax lien may be imposed for delinquent taxes owed on real property or personal property, or as a result of failure to pay income taxes or other taxes.
-- Wikipedia
Legal Definition
A lien acquired by court order that gives the government a security interest in property because of a failure to pay assessed taxes. If the property is mortgaged, a tax lien will take precedence over the mortgage. This is why a mortgage lender may choose to protect the value of its own lien by paying the tax debt and seeking reimbursement from the property owner.
Legal Definition
Arising from not paying taxes on income or property this is the involuntary charge and must be paid first in a case of liquidation.
Legal Definition
A statutory lien, existing in favor of the state or municipality, upon the lands of a person charged with taxes, binding the same either for the taxes assessed upon the specific tract of land or (in some jurisdictions) for all the taxes due from the individual, and which may be foreclosed for non-payment, by judgment of a court or sale of the land.
-- Black's Law Dictionary