will contest

Definition from Nolo’s Plain-English Law Dictionary

A lawsuit challenging the validity of a will or some of its terms after the person who made the will has died. Will contests are quite rare. There are just a few legal grounds for challenging a will. The most common are undue influence by someone close to the deceased person, the deceased person's lack of capacity (understanding) when the will was signed, improper execution (signing and witnessing) of the will, or fraud (forgery, for example). (See also: no-contest clause)

Definition provided by Nolo’s Plain-English Law Dictionary.