Definition of a Trust
In general, a trust is a relationship in which one person holds title to property, subject to an obligation to keep or use the property for the benefit of another.
A trust is formed under state law. You may wish to consult the law of the state in which the organization is organized. Note that for a trust to qualify under section 501(c)(3) of the Code, its organizing document must contain certain language. Publication 557 contains suggested language.