The rate at which Central bank of Country, in case of India it is Reserve bank of India lends money to the commercial bank is referred to Repo rate. Central bank lends money when a Commercial bank has a shortfall of money. Reverse Repo is the rate at which Central bank borrows money from a commercial bank.
Repo rate is used as a monetary tool to control inflation in the economy. An increased Repo rate increases the cost of borrowing money for a commercial bank and so the supply of money is limited and inflation is brought under control.