(a) TreasuryDirect. TreasuryDirect is a book-entry, online system maintained by Treasury for purchasing, holding and conducting permitted transactions in eligible Treasury securities in electronic form as a computer record on the books of Treasury. TreasuryDirect currently provides for the purchase and holding of eligible book-entry savings bonds, zero-percent certificates of indebtedness, and eligible marketable Treasury securities.

(b) Legacy Treasury Direct. The Legacy Treasury Direct system is a non-Internet-based book-entry system maintained by Treasury for holding and conducting permitted transactions in eligible marketable Treasury securities as book-entry products. The terms and conditions for the Legacy Treasury Direct system are found at 31 CFR part 357, subpart C.

(c) Commercial book-entry system. The commercial book-entry system is the book-entry system in which Treasury securities are held in a tiered system through securities intermediaries such as financial institutions or brokerage firms. The regulations governing the commercial book-entry system are found at 31 CFR part 357, subpart B, and may be referred to in that part as Treasury/Reserve Automated Debt Entry System (TRADES).