fiduciary relationship

Definition from Nolo’s Plain-English Law Dictionary

A relationship in which an individual places complete confidence, trust, and reliance in someone who has a fiduciary duty to act for the individual's benefit. A fiduciary relationship need not be formally or legally established; it may be assumed where the fiduciary has superior knowledge and training compared to the person whose affairs the fiduciary is handling.

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