What is the Legal Term for an Assurance?
We aren't quite certain of the term you seek, but it may be promissory estoppel or detrimental reliance. Promissory estoppel is a term used in contract law that applies where, although there may not otherwise be an enforceable contract, because one party has relied on the promise of the other, it would be unfair not to enforce the agreement. Promissory estoppel arises from a promise which the promisor should reasonably expect to induce action or forebearance of a definite and substantial character on the part of the promisee and which does induce such action or forebearance in binding if injustice can be avoided only by enforcement of the promise. Detrimental reliance is a term commonly used to force another to perform their obligations under a contract, using the theory of promissory estoppel. Promissory estoppel may apply when a promise was made; reliance on the promise was reasonable or foreseeable; there was actual and reasonable reliance on the promise; the reliance was detrimental; and injustice can only be prevented by enforcing the promise.
Detrimental reliance must be shown to involve reliance that is reasonable, which is a determination made on an individual case-by-case basis, taking all factors into consideration. Detrimental means that some type of harm is suffered.
Reasonable reliance is usually referred to as a theory of recovery in contract law. It was what a prudent person might believe and act upon based on something told by another. Sometimes a person acts in reliance on the promise of a profit or other benefit, only to learn that the statements or promises were either incorrect or were exaggerated. The one who acted to their detriment in reasonable reliance may recover damages for the costs of his/her actions or demand performance. Reasonable reliance connotes the use of the standard of an ordinary and average person.