Trust is the willingness of one party (the trustor) to become vulnerable to another party (the trustee) on the presumption that the trustee will act in ways that benefit the trustor. In addition, the trustor does not have control over the actions of the trustee. Scholars distinguish between generalized trust (also known as social trust), which is the extension of trust to a relatively large circle of unfamiliar others, and particularized trust, which is contingent on a specific situation or a specific relationship.

As the trustor is uncertain about the outcome of the trustee's actions, the trustor can only develop and evaluate expectations. Such expectations are formed with a view to the motivations of the trustee, dependent on their characteristics, the situation, and their interaction. The uncertainty stems from the risk of failure or harm to the trustor if the trustee does not behave as desired.

In the social sciences, the subtleties of trust are a subject of ongoing research. In sociology and psychology, the degree to which one party trusts another is a measure of belief in the honesty, fairness, or benevolence of another party. The term "confidence" is more appropriate for a belief in the competence of the other party. A failure in trust may be forgiven more easily if it is interpreted as a failure of competence rather than a lack of benevolence or honesty. In economics, trust is often conceptualized as reliability in transactions. In all cases, trust is a heuristic decision rule, allowing the human to deal with complexities that would require unrealistic effort in rational reasoning.