: of, relating to, or involving a confidence or trust: as
a : held or founded in trust or confidence
b : holding in trust
c : depending on public confidence for value or currency
A fiduciary is a person in a position of trust who obligates himself to always act in the best interests of those who trust him. For example, the trustee of a trust is considered a fiduciary and must always act in the best interests of the trust's beneficiaries. Fiduciaries are legally required to act in the best interests of those they're serving, and they can never put their own interests first.
Many stockbrokers, insurance agents, and buying/selling agents, though not held to a fiduciary standard legally, still strive to do what is best for their clients. It is prudent, however, to be aware of what a fiduciary is. Fiduciaries serve a dual role in putting their clients' best interests before their own, as well as setting a good example for those who aren't obligated to do so.
There are very clear guidelines on who is considered a fiduciary in the financial world, and who is not.
People in the following groups are considered fiduciaries:
Real Estate Agents acting on your behalf
Advisors in this group are legally required to act and advise you only for your benefit and interests. They can never act in a way that is contrary to what is best for you. They must act with undivided loyalty to you. If they fail to do so, you are entitled to legal action against them. It's not enough for them to just provide "suitable" recommendations. They must try their hardest to provide you with the best advice possible.
The following people are not considered fiduciaries:
Real Estate Agents acting on the other party's behalf
"Advisors" in this group do not represent you. They generally represent their company. They have no legal responsibility to act in your best interest. However, they are not permitted to commit fraud or provide you with "unsuitable" recommendations. But the "unsuitable" standard is very broad and difficult to impose.