restraint; a bar. Estoppel arises where a person has done some act that the policy of the law will not permit him to deny, or where circumstances are such that the law will not permit a certain argument because it would lead to an unjust result. In the context of contract law, for example, one is estopped from denying existence of a binding contract where one has done something intending that another rely on his conduct, and the result of the reliance is detrimental to that other person.