An attorney's lien is a financial lien that is placed by an attorney against a client who has not paid for their legal services for the purpose of forcing the client to pay. It is a lien in the same sense as any normal person takes a lien against another, but is with respect to legal fees only.
An attorney would have to satisfy all of the normal conditions brought about by law when placing a lien on a client's property including first trying normal recourse methods for payment of fees and services rendered including going through collection methods.