Estoppel

“A rule of law that when person A, by act or words, gives person B reason to believe a certain set of facts upon which person B takes action, person A cannot later, to his (or her) benefit, deny those facts or say that his (or her) earlier act was improper.”

If still you need more explanations the use URL given below;

https://www.duhaime.org/LegalDictionary/E/Estoppel.aspx