Refers to United States securities law regulation (17 CFR §§ 230.501-230.508) setting forth under safe harbor exemption of section 5 of the Securities Act of 1933 (15 U.S.C. §77a et seq.), to the need to avoid the expensive process of filing a registration statement with the SEC. Regulation D is usually used for selling shares in startup companies and closely held businesses. Usually a Form D must be filed to take advantage of Regulation D. See Accredited Investor.