What is the meaning of the legal word 'estoppel by conduct' ?

Estoppel by conduct, also called equitable estoppel or estoppel in pais, stops a person who by words or conduct has led another to believe a thing and act on it from later denying that thing.

It has no connection with an estate; in Indian law the rule appears in section 115 of the Indian Evidence Act, 1872 (now section 121 of the Bharatiya Sakshya Adhiniyam, 2023).