A Repurchase Agreement (aka repo) allows a borrower to use a financial security as collateral for a cash loan at a fixed rate of interest. The borrower agrees to sell immediately a security to a lender and also agrees to buy the same security from the lender at a fixed price at some later date.
3 types of repo maturities: overnight, term, and open repo. Overnight: a one-day maturity transaction. Term: a specified end date. Open: no end date.
In a tri-party repo, a custodian bank or international clearing organization (the tri-party agent) acts as an intermediary between the two parties to the repo. The tri-party agent is responsible for the administration of the transaction including collateral allocation, marking to market, and substitution of collateral.
(source: wikipedia, marketplace whiteboard)