A fiduciary is generally a person you trust. A fiduciary relationship is formed between two parties who trust each other. The trust typically has to do with assets, money or property.
 
In real estate, a fiduciary relationship is created between a real estate agent, known as the fiduciary, and a buyer or a seller, known as the principal. A buyer's agent, for example, works on behalf of the buyer and must hold that buyer's interests above the interests of the agent. That trust created requires the highest standard of care and loyal treatment to the buyer.
 
Similarly, a seller's agent can be placed into a fiduciary relationship with the seller through an Exclusive Listing Agreement. As such, a seller's agent cannot tell a buyer whether the seller will accept less or divulge any other personal information about the seller to the buyer without the seller's express written permission.
 
A buyer broker's agreement establishes a legal document between the buyer and the buyer's broker / agent, which spells out the fiduciary duties of each party. Once a fiduciary has been breached, for example, the buyer no longer trusts the agent, that fiduciary relationship can be considered broken, and buyer's agent might be in a position of authority to cancel the contract, and vice versa.