Cash reserve Ratio (CRR) is the amount of funds that the banks have to keep with the RBI. If the central bank decides to increase the CRR, the available amount with the banks comes down. The RBI uses the CRR to drain out excessive money from the system.
Scheduled banks are required to maintain with the RBI an average cash balance, the amount of which shall not be less than 4% of the total of the Net Demand and Time Liabilities (NDTL), on a fortnightly basis.
Reverse Repo rate is the rate at which the RBI borrows money from commercial banks. Banks are always happy to lend money to the RBI since their money are in safe hands with a good interest.
An increase in reverse repo rate can prompt banks to park more funds with the RBI to earn higher returns on idle cash. It is also a tool which can be used by the RBI to drain excess money out of the banking system.
The rate at which the RBI lends money to commercial banks is called repo rate. It is an instrument of monetary policy. Whenever banks have any shortage of funds they can borrow from the RBI.
A reduction in the repo rate helps banks get money at a cheaper rate and vice versa. The repo rate in India is similar to the discount rate in the US.