tenancy by estoppel

Tenancy that remains in effect despite the fact that its grantor had no legal right to grant it; such as when a mortgagor in possession of the mortgaged property grants a lease on it against the terms of the mortgage deed or the statutory provisions. This lease still binds the tenant and, under the doctrine of estoppel, the mortgagor may sue for the unpaid rent. If the mortgagor subsequently reacquires the ownership of the property (and thereby the legal right to grant the tenancy) the tenancy by estoppel becomes an entirely legal tenancy.