open box
Open Box
2. Collateral used to secure funds borrowed on a margin account. A margin account allows an investor to buy securities with money borrowed from a broker; the funds are payable on demand of the broker. They also must be secured by an open box, which usually consists of securities owned by the borrower. The "box" refers to a safe where the stock and bond certificates are kept until the margin account is paid off. An open box in this sense is also called an active box.