Definitions of estoppel

a principle that prevents someone from making actions, statements or promises that are the opposite of what that person has earlier said, promised or otherwise implied (=suggested without saying it directly) or done, or that go against a finding of a court of law, especially when this would result in loss or harm to another person

To establish estoppel, the plaintiff must show that she was, in some manner, misled by the acts or statements of the defendant.