the doctrine designed to protect a party from the detriment which would flow from that party's change of position if the assumption or expectation that led to it were to be rendered groundless by another: Waltons Stores (Interstate) Ltd v Maher (1988) 164 CLR 387; 76 ALR 513. Estoppels are recognised both at common law and in equity. The concept of unconscionability has unified and rationalised the various types of estoppel, which are no longer seen as a series of independent rules: Commonwealth v Verwayen (1990) 170 CLR 394; 95 ALR 321. Some estoppels operate a substantive rules of law; others as evidentiary rules. See also Common law estoppel; Contract; Detriment; Estoppel by representation; Estoppel in pais; Issue estoppel; Promissory estoppel; Proprietary estoppel; Reliance.

(Ref: Butterworths Concise Australian Legal Dictionary)