Reserve Bank of Australia - Domestic Market Operations 

Note: The RBA changed the time of its first round of Open Market Operations (OMO) from 9.30-9.45 am to 9.20-9.35 am on Monday 27 November 2017.
As part of its responsibility for monetary policy, the Reserve Bank Board sets a target for the cash rate. This is the rate at which banks borrow from and lend to each other on an overnight, unsecured basis. The rate is determined by the demand and supply of exchange settlement balances that commercial banks hold at the Reserve Bank. Through its open market operations, the Reserve Bank alters the volume of these balances so as to keep the cash rate as close as possible to its target.
Guy Debelle, Former Assistant Governor (Financial Markets)