A claim for money owing, registered against a property.
A lien does not imply that payment is overdue, simply that the total amount has not yet been paid.
The purpose of a lien is to protect the beneficiary's ability to recover their money if the property owner fails to make the expected payments.
For example, if you have someone install a furnace and are paying their fees over a period of 6 months, they may register a "mechanics lien" on your property. This protects their right to recover the furnace if you do not make all of your payments.
If you were to sell the property, you would have to pay the remaining amount of the lien before selling, or it would be deducted from the selling price.
Other types of lien include a construction lien (when an addition or renovation has been made to a house), and a tax lien (when property taxes or income taxes have not been paid).
A lien is a type of encumbrance.