26 U.S. Code § 856 – Definition of real estate investment trust

(a)In general
For purposes of this title, the term “real estate investment trust” means a corporation, trust, or association—
(1)which is managed by one or more trustees or directors;
(2)the beneficial ownership of which is evidenced by transferable shares, or by transferable certificates of beneficial interest;
(3)which (but for the provisions of this part) would be taxable as a domestic corporation;
(4)which is neither (A) a financial institution referred to in section 582(c)(2), nor (B) an insurance company to which subchapter L applies;
(5)the beneficial ownership of which is held by 100 or more persons;
(6)subject to the provisions of subsection (k), which is not closely held (as determined under subsection (h)); and
(7)which meets the requirements of subsection (c).

https://www.law.cornell.edu/uscode/text/26/856