The doctrine of estoppel states that when a person has asserted a certain position previously, he or she is prevented from taking an alternative position that is different from the initial one they took. It prevents people from taking a contradictory position from what they had previously said or agreed to by law.
One form of estoppel is promissory estoppel and this is usually found in contract law. If a person (A) acted on another person’s (B)’s promise and as a result, suffers an economic loss because B did not fulfil that promise, then promissory estoppel would protect A from that economic loss.
In essence, estoppel prevents an individual from being unfairly wronged by another person’s failure to honour a promise.
Other types of estoppel include collateral estoppel, estoppel by deed and equitable estoppel.