An individual or group plan that provides, or pays the cost of, medical care (as defined in section 2791(a)(2) of the PHS Act, 42 U.S.C. 300gg-91(a)(2)).

 (1) Health plan includes the following, singly or in combination: 
        (i) A group health plan, as defined in this section. 
        (ii) A health insurance issuer, as defined in this section. 
        (iii) A Health Maintenance Organization (HMO), as defined in this section. 
        (iv) Part A or Part B of the Medicare program under title XVIII of the Social Security Act.
        (v) The Medicaid program under title XIX of the Social Security Act, 42 U.S.C. 1396, et seq. 
        (vi) The Voluntary Prescription Drug Benefit Program under Part D of title XVIII of the Act, 42 U.S.C. 1395w-101 through 1395w-152.
        (vii) An issuer of a Medicare supplemental policy (as defined in section 1882(g)(1) of the Social Security Act, 42 U.S.C. 1395ss(g)(1)). 
        (viii) An issuer of a long-term care policy, excluding a nursing home fixed-indemnity policy.
        (ix) An employee welfare benefit plan or any other arrangement that is established or maintained for the purpose of offering or providing health benefits to the employees of two or more employers. 
        (x) The healthcare program for active military personnel under title 10 of the United States Code. 
        (xi) The veterans’ healthcare program under 38 U.S.C. chapter 17. 
        (xii) The Indian Health Service program under the Indian Healthcare Improvement Act, 25 U.S.C. 1601, et seq.
        (xiii) The Federal Employees Health Benefits Program under 5 U.S.C. 8902, et seq. 
        (xiv) An approved State child health plan under title XXI of the Social Security Act, providing benefits for child health assistance that meet the requirements of section 2103 of the Social Security Act, 42 U.S.C. 1397, et seq. 
        (xv) The Medicare Advantage program under Part C of title XVIII of the Social Security Act, 42 U.S.C. 1395w-21 through 1395w-28.
        (xvi) A high-risk pool that is a mechanism established under State law to provide health insurance coverage or comparable coverage to eligible individuals.
        (xvii) Any other individual or group plan, or combination of individual or group plans, that provides or pays for the cost of medical care (as defined in section 2791(a)(2) of the PHS Social Security Act, 42 U.S.C. 300gg-91(a)(2)).

 (2) Health plan excludes: 
        (i) Any policy, plan, or program to the extent that it provides, or pays for the cost of, excepted benefits that are listed in section 2791(c)(1) of the PHS Act, 42 U.S.C. 300gg-91(c)(1); and 
        (ii) A government-funded program (other than one listed in paragraph (1)(i)-(xvi) of this definition):

                (A) Whose principal purpose is other than providing, or paying the cost of, healthcare; or 
                (B) Whose principal activity is: 

                        (1) The direct provision of healthcare to persons; or 
                        (2) The making of grants to fund the direct provision of healthcare to persons.
Sources:
NIST SP 800-66r2 under health plan from HIPAA Security Rule