Complex sentence: Regulation D (also known as Reg D) is a regulation of the U.S. Securities and Exchange Commission (the "SEC"), and is also a term for an investment strategy, mostly associated with hedge funds, based upon that regulation.
Split into simpler sentences: Regulation D (also known as Reg D) is a regulation of the U.S. Securities and Exchange Commission (the "SEC"). It also refers to an investment strategy, mostly associated with hedge funds, based upon that regulation.