Fiduciary is a term that refers to someone who has a legal or ethical responsibility to act in the best interest of another. It's most commonly used to describe a financial advisor, who has a legal obligation to act in the best interest of their clients—as opposed to the best interest of the clients' money. It means that if any conflicts of interest arise, they must be disclosed and resolved before doing anything else.
If you're looking for an unbiased opinion on your financial situation, it's worth taking the time to find an advisor who is a fiduciary. Many advisors will claim they're acting in your best interest, but not all are held to that same standard. Just because someone is licensed to sell investment products doesn't mean they're required or even legally able to act in your best interest. That's why it's important to have an appointment with someone who does have that obligation.