A repurchase agreement, also known as a repo, RP, or sale and repurchase agreement, is a form of secured short-term borrowing, usually, though not always, using government securities as collateral. A contracting party sells a security to a lender and, by agreement between the two parties, repurchases the security back shortly afterwards, at a slightly higher contracted price. The difference in the prices and the time interval between sale and repurchase creates an effective interest rate on the loan. The mirror transaction, a "reverse repurchase agreement," is a form of secured contracted lending in which a party buys a security along with a concurrent commitment to sell the security back in the future at a specified time and price. Because this form of funding is often used by dealers, the convention is to reference the dealer's position in a transaction with a counterparty. Central banks also use repo and reverse repo transactions to manage banking system reserves. When the Federal Reserve borrows funds to drain reserves, it can do so by selling a government security from its inventory with a commitment to buy it back in the future; it calls the transaction a reverse repo because the dealer counterparty to the Fed is lending money. Similarly, when the Federal Reserve wishes to add to banking reserves, it can buy a government security with a forward commitment to sell it back. It calls this transaction a repo because the Fed counterparty is borrowing money.