An express mechanic's lien is a security interest in property that is granted to someone who has done some work on that property. Those with specific questions on liens should consult a real estate attorney.
Liens come in various types, but all of them represent an interest in property that a court awards to a non-owner in order to make sure that the owner pays some debt or obligation. Unpaid liens will often delay or prevent sale of the property.
Mechanic's liens can be placed on real or personal property. Those who do repair or maintenance work on the property may seek a mechanic's lien in order to make sure that they receive payment for the work. Automotive repairmen and residential contractors are common mechanic's lienholders.
An express mechanic's lien is one which is granted specifically by some contract or agreement. For example, if a contractor agrees to paint Bob's house, the contract between the two may specifically grant the contractor a lien on the house in the event that Bob fails to pay.