Estoppel's a legal doctrine at common law, where a party's barred from claiming or denying an argument on an equitable ground. Estoppel complements the requirement of consideration in contract law. In general, estoppel protects an aggrieved party, if the counter-party induced an expectation from the aggrieved party, and the aggrieved party reasonably relied on the expectation and would suffer detriment if the expectation isn't met. While there're many types of estoppel, in simpler terms, most e… (More on Estoppel)