D.C. Code § 4-631

For the purposes of this chapter, the term “health insurer” means any person that provides one or more health benefit plans or insurance in the District of Columbia, including an insurer, a hospital and medical services corporation, a fraternal benefit society, a health maintenance organization, a multiple employer welfare arrangement, or any other person providing a plan of health insurance subject to the authority of the Commissioner of the Department of Insurance, Securities, and Banking.