This section is from the book "Popular Law Library Vol7 Equity Jurisprudence, Trusts, Equity Pleading", by Albert H. Putney. Also available from Amazon: Popular Law-Dictionary.
"An equitable lien is not an estate or property in the thing itself, nor a right to recover the thing, that is, a right which may be the basis of a possessory action; it is neither a jus ad rem nor a jus in re. It is simply a right of a special nature over the thing, which constitutes a charge or encumbrance upon the thing, so that the very thing itself may be proceeded against in an equitable action, and either sold or sequestered under a judicial decree, and its proceeds in the one case, or its rents and profits in the other, applied upon the demand of the creditor in whose favor the lien exists. It is the very essence of this condition that while the lien continues the possession of the thing remains with the debtor or the person who holds the proprietary interest, subject to the encumbrance. The equitable lien differs essentially from the common law lien, which is simply a right to retain possession of the chattel until some debt or demand due to the person thus retaining is satisfied; and possession is such an inseparable element, that if it be voluntarily surrendered by the creditor, the hen is at once extinguished." 2
1 See Subject 21, in this Volume.
The most important classes of equitable liens are vendor's and vendee's liens.
A vendor's hen arises where property is sold and transferred, but a part or the whole of the purchase price left unpaid. Here the vendor will have a lien on the property for the amount due him. The taking of other security destroys this hen, and as this is almost invariably done (on account of the insecurity of the vendor's hen), this hen is at present of little importance.
The vendee's lien arises where the vendee, under a contract for the purchase of land, pays a part, or the whole of the purchase price before conveyance.