Open market operations
(OMOs or OMO).
The buying or selling of financial securities in the open market by a central bank to influence the amount of money in circulation.
The range of instruments used by central banks has tended to increase following the financial crisis early in the 21st Century.
For example, the European Central Bank operates through Euro-member states' National Central Banks (NCBs). It lists as available to an NCB "reverse transactions" that are applicable on the basis of repurchase agreements or collateralised loans, outright transactions, issuance of debt certificates, foreign exchange swaps and collection of fixed-term deposits.